Change search
Refine search result
123 1 - 50 of 125
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ostlin, Goeran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Probing Cluster Formation under Extreme Conditions: Super Star Clusters in Blue Compact GalaxiesManuscript (preprint) (Other academic)
    Abstract [en]

    The numerous and massive young star clusters in blue compact galaxies (BCG) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between the cluster population and their hosts, such as the cluster specific luminosity in the U band, TL(U), and the star formation rate density ΣSFR; the V bandluminosity of the brightest youngest cluster, Mbrightest, and the mean star formation Vrate (SFR); the cluster formation efficiency versus the ΣSFR. We find that BCGs fairly well reproduce the relations, supporting a scenario where cluster formation and environmental properties of the host are correlated. They occupy, in all the diagrams, the regions of higher SFRs, suggesting the extreme nature of the starburst operating in these systems. We suggest that the BCG environment has most likely favoured the compression and collapse of the giant molecular clouds, enhancing the local star formation efficiency, so that massive clusters have been formed. The cluster formation efficiency (i.e., the fraction of star formation happening in star clusters) in BCGs is higher than the 8-10 % reported from quiescent spirals and dwarf starburst galaxies. BCGs have a cluster formation efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the averaged value is ∼ 30 %).

  • 2.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ryon, J. E.
    Messa, Matteo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kim, H.
    Grasha, K.
    Cook, D. O.
    Calzetti, D.
    Lee, J. C.
    Whitmore, B. C.
    Elmegreen, B. G.
    Ubeda, L.
    Smith, L. J.
    Bright, S. N.
    Runnholm, Axel
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Andrews, J. E.
    Fumagalli, M.
    Gouliermis, D. A.
    Kahre, L.
    Nair, P.
    Thilker, D.
    Walterbos, R.
    Wofford, A.
    Aloisi, A.
    Ashworth, G.
    Brown, T. M.
    Chandar, R.
    Christian, C.
    Cignoni, M.
    Clayton, G. C.
    Dale, D. A.
    de Mink, S. E.
    Dobbs, C.
    Elmegreen, D. M.
    Evans, A. S.
    Gallagher, J. S.
    Grebel, E. K.
    Herrero, A.
    Hunter, D. A.
    Johnson, K. E.
    Kennicutt, R. C.
    Krumholz, M. R.
    Lennon, D.
    Levay, K.
    Martin, C.
    Nota, A.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pellerin, A.
    Prieto, J.
    Regan, M. W.
    Sabbi, E.
    Sacchi, E.
    Schaerer, D.
    Schiminovich, D.
    Shabani, F.
    Tosi, M.
    Van Dyk, S. D.
    Zackrisson, E.
    Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 6282017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 841, no 2, article id 131Article in journal (Refereed)
    Abstract [en]

    We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes similar to-2 and a truncation of a few times 10(5) M-circle dot. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find massindependent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (<= 10(4) M-circle dot) clusters, suggesting that a massdependent component is necessary to fully describe the YSC disruption process in NGC 628.

  • 3.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hayes, M.
    Observatory of Geneva, Switzerland.
    On the Origin of the Red Excess in Very Young Super Star Clusters: The Case of SBS 0335-052E2010In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 725, no 2, p. 1620-1628Article in journal (Refereed)
    Abstract [en]

    The spectral energy distribution analysis of very young unresolved star clusters challenges our understanding of the cluster formation process. Studies of resolved massive clusters in the Milky Way and in the nearby Magellanic Clouds show us that the contribution from photoionized gas is very important during the first Myr of cluster evolution. We present our models which include both a self-consistent treatment of the photoionized gas and the stellar continuum and quantify the impact of such a nebular component on the total flux of young unresolved star clusters. A comparison with other available models is considered. The very young star clusters in the SBS 0335-052E dwarf starburst galaxy are used as a test for our models. Due to the low metallicity of the galactic medium our models predict a longer lasted nebular phase which contributes between 10% and 40% of the total near-infrared (NIR) fluxes at around 10 Myr. We thus propose a possible solution for the observed flux excess in the six bright super star clusters (SSCs) of SBS 0335-052E. Reines et al. showed that the observed cluster fluxes, in the red-optical and NIR range, sit irreconcilably above the stellar continuum models provided. We find that in the age range estimated from the Hα emission we can explain the red excess in all six SSCs as due to nebular emission, which at cluster ages around 10 Myr still affects the NIR wavebands substantially.

  • 4. Adamo, Angela
    et al.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bastian, N.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Livermore, R. C.
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy.
    HIGH-RESOLUTION STUDY OF THE CLUSTER COMPLEXES IN A LENSED SPIRAL AT REDSHIFT 1.5: CONSTRAINTS ON THE BULGE FORMATION AND DISK EVOLUTION2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 766, no 2, p. 105-Article in journal (Refereed)
    Abstract [en]

    We analyze the clump population of the spiral galaxy Sp 1149 at redshift 1.5. Located behind the galaxy cluster MACS J1149.5+2223, Sp 1149 has been significantly magnified allowing us to study the galaxy on physical scales down to similar to 100 pc. The galaxy cluster frame is among the targets of the Cluster Lensing And Supernova survey with Hubble (CLASH), an ongoing Hubble Space Telescope (HST) Multi-Cycle Treasury program. We have used the publicly available multi-band imaging data set to reconstruct the spectral energy distributions of the clumps in Sp 1149, and derive, by means of stellar evolutionary models, their physical properties. We found that 40% of the clumps observed in Sp 1149 are older than 30 Myr and can be as old as 300 Myr. These are also the more massive (luminous) clumps in the galaxy. Among the complexes in the local reference sample, the star-forming knots in luminous blue compact galaxies could be considered progenitor analogs of these long-lived clumps. The remaining 60% of clumps have colors comparable to local cluster complexes, suggesting a similar young age. We observe that the Sp 1149 clumps follow the M proportional to R-2 relation similar to local cluster complexes, suggesting similar formation mechanisms although they may have different initial conditions (e.g., higher gas surface densities). We suggest that the galaxy is experiencing a slow decline in star formation rate and a likely transitional phase toward a more quiescent star formation mode. The older clumps have survived between 6 and 20 dynamical times and are all located at projected distances smaller than 4 kpc from the center. Their current location suggests migration toward the center and the possibility of being the building blocks of the bulge. On the other hand, the dynamical timescale of the younger clumps is significantly shorter, meaning that they are quite close to their birthplace. We show that the clumps of Sp 1149 may account for the expected metal-rich globular cluster population usually associated with the bulge and thick disk components of local spirals.

  • 5.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Probing cluster formation under extreme conditions: massive star clusters in blue compact galaxies2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 417, no 3, p. 1904-1912Article in journal (Refereed)
    Abstract [en]

    The numerous and massive young star clusters in blue compact galaxies (BCGs) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between cluster populations and their hosts, such as the fraction of the total luminosity contributed by the clusters as function of the mean star formation rate (SFR) density, the V-band luminosity of the brightest youngest cluster as related to the mean host SFR and the cluster formation efficiency (i.e. the fraction of star formation happening in star clusters) versus the density of the SFR. We find that BCGs follow the trends, supporting a scenario where cluster formation and environmental properties of the host are correlated. They occupy, in all the diagrams, the regions of higher SFRs, as expected by the extreme nature of the starbursts operating in these systems. We find that the star clusters contribute almost to the 20 per cent of the UV luminosity of the hosts. We suggest that the BCG starburst environment has most likely favoured the compression and collapse of the giant molecular clouds, enhancing the local star formation efficiency, so that massive clusters have been formed. The estimated cluster formation efficiency supports this scenario. BCGs have a cluster formation efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the averaged value is similar to 35 per cent) which is much higher than the 8-10 per cent reported for quiescent spirals and dwarf star-forming galaxies.

  • 6.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Probing the near-IR flux excess in young star clusters2011Conference paper (Refereed)
    Abstract [en]

    We report the results of a recent study of young star clusters (YSCs) in luminous blue compact galaxies (BCGs). The age distributions of the YSCs suggest that the starburst episode in Haro 11, ESO 185-IG13, and Mrk 930 started not more than 30-40 Myr ago. A peak of cluster formation only 3 - 4 Myr old is observed, unveiling a unique sample of clusters still partially embedded. A considerable fraction of clusters (30 - 50%), mainly younger than 10 Myr, shows an observed flux excess between 0.8 and 2.2 micron. This so-called near-infrared (NIR) excess is impossible to reproduce even with the most recent spectral synthesis models (that include a self-consistent treatment of the photoionized gas). We have used these YSCs to probe the very early evolution phase of star clusters. In all the three host galaxies, the analysis is limited to the optically brightest objects, i.e., systems that are only partially embedded by their natal cocoons (since deeply embedded clusters are probably too faint to be detected). We discuss possible explanations for this NIR excess, in the context of IR studies of both extragalactic young star clusters and resolved massive star forming regions in the Milky Way and in the nearby Magellanic Clouds.

  • 7.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hayes, Matthew
    The Extremely Young Star Cluster Population In Haro 112010In: Galaxy Wars: Star Formation and Stellar Populations in Interacting Galaxies / [ed] Beverly Smith, James Higdon, Sarah Higdon, and Nathan Bastian, San Francisco: Astronomical Society of the Pacific , 2010, p. 74-Conference paper (Refereed)
    Abstract [en]

    We have performed a deep multi-band photometric analysis of the star cluster population of Haro 11. This starburst galaxy (log L_FUV = 10.3 L_sun) is considered a nearby analogue of Lyman break galaxies (LBGs) at high redshift. The study of the numerous star clusters in the systems is an effective way to investigate the formation and evolution of the starburst phase. In fact, the SED fitting models have revealed a surprisingly young star cluster population, with ages between 0.5 and 40 Myr, and estimated masses between 10^3 and 10^7 solar masses. An independent age estimation has been done with the EW(Halpha) analysis of each cluster. This last analysis has confirmed the young ages of the clusters. We noticed that the clusters with ages between 1 and 10 Myr show a flux excess in H (NIC3/F160W) and/or I (WFPC2/F814W) bands with respect to the evolutionary models. Once more Haro 11 represents a challenge to our understanding.

  • 8.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hayes, Matthew
    The Massive Star Clusters in the Dwarf Merger ESO 185-IG13: is the Red Excess Ubiquitous in Starbursts?2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 414, no 3, p. 1793-1812Article in journal (Other academic)
    Abstract [en]

    We have investigated the starburst properties of the luminous blue compact galaxy ESO 185-IG13. The galaxy has been imaged with the high resolution cameras onboard to the Hubble Space Telescope. From the UV to the IR, the data reveal a system shaped by hundreds of young star clusters, and fine structures, like a tidal stream and a shell. The presence of numerous clusters and the perturbed morphology indicate that the galaxy has been involved in a recent merger event. Using previous simulations of shell formation in galaxy mergers we constrain potential progenitors of ESO 185-IG13. The analysis of the star cluster population is used to investigate the properties of the present starburst and to date the final merger event, which has produced hundreds of clusters younger than 100 Myr. We have found a peak of cluster formation only 3.5 Myr old. A large fraction of these clusters will not survive after 10-20 Myr, due to the "infant mortality" caused by gas expulsion. However, this sample of clusters represents an unique chance to investigate the youngest phases of cluster evolution. As already observed in the analog blue compact galaxy Haro 11, a fraction of young clusters are affected by a flux excess at wavelengths longer than 8000 \AA. Ages, masses, and extinctions of clusters with this NIR excess are estimated from UV and optical data. We discuss similarities and differences of the observed NIR excess in ESO 185-IG13 clusters with other cases in the literature. The cluster ages and masses are used to distinguish among the potential causes of the excess. We observe, as in Haro 11, that the use of the IR and the (commonly used) I band data results in overestimates of age and mass in clusters affected by the NIR excess. This has important implications for a number of related studies of star clusters.

  • 9.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Hayes, Matthew
    Tracing the star formation history of three Blue Compact galaxies through the analysis of their star clusters2009Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    We present preliminary results from a study of the compact star cluster populations in three local luminous blue compact galaxies: ESO 185-IG 013, ESO 350-IG 038 (a.k.a. Haro 11), and MRK 930. These systems show peculiar morphologies and the presence of hundreds of SCs that have been produced by the past, recent, and/or current starburst phases. We use a complete set of HST images ranging from the UV to IR for each galaxy. Deep images in V (WFPC2/f606w) and I (WFPC2/f814w) are used to capture most of the star cluster candidates up to the old ones (fainter) which have had, in the past, less possibility to be detected. The other bands are used in the SED fitting technique for constraining ages and masses. Our goals are to investigate the evolution of these three blue compact galaxies and the star cluster formation impact on their star formation history.

  • 10.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hayes, Matthew
    Observatoire Astronomique de l'Université de Genève.
    Cumming, Robert
    Stockholm University, Faculty of Science, Department of Astronomy.
    Micheva, Genoveva
    Stockholm University, Faculty of Science, Department of Astronomy.
    Super star clusters in Haro 11: properties of a very young starburst and evidence for a near-infrared flux excess2010In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, MNRAS, Vol. 407, no 2, p. 870-890Article in journal (Refereed)
    Abstract [en]

    We have used multiband imaging to investigate the nature of an extreme starburst environment in the nearby Lyman break galaxy analogue Haro 11 (ESO350-IG038) by means of its stellar cluster population. The central starburst region has been observed in eight different high-resolution Hubble Space Telescope (HST) wavebands, sampling the stellar and gas components from UV to near-infrared. Photometric imaging of the galaxy was also carried out at 2.16μm by NaCo AO instrument at the ESO Very Large Telescope. We constructed integrated spectral energy distributions (SEDs) for about 200 star clusters located in the active star-forming regions and compared them with single stellar population models (suitable for physical properties of very young cluster population) in order to derive ages, masses and extinctions of the star clusters. The cluster age distribution we recover confirms that the present starburst has lasted for 40Myr, and shows a peak of cluster formation only 3.5 Myr old. With such an extremely young cluster population, Haro 11 represents a unique opportunity to investigate the youngest phase of the cluster formation process and evolution in starburst systems. We looked for possible relations between cluster ages, extinctions and masses. Extinction tends to diminish as a function of the cluster age, but the spread is large and reaches the highest dispersion for clusters in partial embedded phases (<5Myr). A fraction of low-mass (below 104 Msolar), very young (1-3Myr) clusters is missing, either because they are embedded in the parental molecular cloud and heavily extinguished, or because of blending with neighbouring clusters. The range of the cluster masses is wide; we observe that more than 30 per cent of the clusters have masses above 105 Msolar, qualifying them as super star clusters. Almost half of the cluster sample is affected by flux excesses at wavelengths >8000Å which cannot be explained by simple stellar evolutionary models. Fitting SED models over all wavebands leads to systematic overestimates of cluster ages and incorrect masses for the stellar population supplying the light in these clusters. We show that the red excess affects also the HST F814W filter, which is typically used to constrain cluster physical properties. The clusters which show the red excess are younger than 40Myr we discuss possible physical explanations for the phenomenon. Finally, we estimate that Haro 11 has produced bound clusters at a rate almost a factor of 10 higher than the massive and regular spirals, like the Milky Way. The present cluster formation efficiency is ~38 per cent of the galactic star formation rate.

  • 11.
    Adamo, Angela
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Papaderos, P.
    Bergvall, N.
    Rich, R. M.
    Micheva, Genoveva
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburst2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 415, no 3, p. 2388-2406Article in journal (Refereed)
    Abstract [en]

    We present the analysis of the large population of star clusters in the blue compact galaxy (BCG) Mrk 930. The study has been conducted by means of a photometric analysis of multiband data obtained with the Hubble Space Telescope (HST). We have reconstructed the spectral energy distributions of the star clusters and estimated the age, mass and extinction for a representative sample. Similar to previous studies of star clusters in BCGs, we observe a very young cluster population with 70 per cent of the systems formed less than 10 Myr ago. In Mrk 930, the peak in the star cluster age distribution at 4 Myr is corroborated by the presence of Wolf-Rayet spectral features, and by the observed optical and infrared (IR) line ratios [OIII]/H beta and [Ne III]/[Ne II]. The recovered extinction in these very young clusters shows large variations, with a decrease at older ages. It is likely that our analysis is limited to the optically brightest objects (i.e. systems only partially embedded in their natal cocoons; the deeply embedded clusters being undetected). We map the extinction across the galaxy using low-resolution spectra and the H alpha-to-H beta ratio, as obtained from ground-based narrow band imaging. These results are compared with the extinction distribution recovered from the clusters. We find that the mean optical extinction derived in the starburst regions is close to the averaged value observed in the clusters [more than 80 per cent of the systems have E(B - V) <= 0.2mag], but locally, do not trace the more extinguished clusters. Previous HST studies of BCGs have revealed a population of young and extremely red super star clusters. We detect a considerable fraction of clusters affected by a red excess also in Mrk 930. The nature of the red excess, which turns up at near-IR wavelengths (I band and longwards), remains unknown. We compare the cluster formation history and the star formation history, the latter derived from the fit of spectral population synthesis models to the spectra. We find a general agreement between the two independently estimated quantities. Using the cluster properties, we perform a study of the host environmental properties. We find that the cluster formation efficiency (the fraction of star formation happening in clusters) is significantly higher, suggesting a key role of the environment for the formation of these massive objects.

  • 12.
    Amanullah, Rahman
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ferretti, Raphael
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Papadogiannakis, Seméli
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Petrushevska, Tanja
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Brown, P. J.
    Cao, Y.
    Contreras, C.
    Dahle, H.
    Elias-Rosa, N.
    Fynbo, J. P. U.
    Gorosabel, J.
    Guaita, L.
    Hangard, Laura
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Howell, D. A.
    Hsiao, E. Y.
    Kankare, E.
    Kasliwal, M.
    Leloudas, G.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mattila, S.
    Nugent, P.
    Phillips, M. M.
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stanishev, V.
    Sullivan, M.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Asadi, Saghar
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Herrero-Illana, R.
    Jensen, J. J.
    Karhunen, K.
    Lazarevic, S.
    Varenius, E.
    Santos, P.
    Sridhar, S. Seethapuram
    Wallström, S. H. J.
    Wiegert, J.
    Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 mu m2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 453, no 3, p. 3300-3328Article in journal (Refereed)
    Abstract [en]

    We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2-2 mu m. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B - V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction R-V. In particular, we note that for the two SNe with E(B - V) greater than or similar to 1 mag, for which the colour excess is dominated by dust extinction, we find R-V = 1.4 +/- 0.1 and R-V = 2.8 +/- 0.1. Adding UV photometry reduces the uncertainty of fitted R-V by similar to 50 per cent allowing us to also measure R-V of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe.

  • 13.
    Andreas, Sandberg
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bik, Adrianus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guaita, L.
    Limits on Lyman Continuum Escape from z = 2.2 Hα-emitting Galaxies2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 814, no 1, article id L10Article in journal (Refereed)
    Abstract [en]

    The leakage of Lyman continuum (LyC) photons from star-forming galaxies is an elusive parameter. When observed, it provides a wealth of information on star formation in galaxies and on the geometry of the interstellar medium, and puts constraints on the role of star-forming galaxies in the reionization of the universe. Hα-selected galaxies at  trace the highest star formation population at the peak of cosmic star formation history, providing a base for directly measuring LyC escape. Here we present this method and highlight its benefits as well as caveats. We also use the method on 10 Hα emitters in the Chandra Deep Field South at  also imaged with the Hubble Space Telescope in the ultraviolet. We find no individual LyC detections, and our stack puts a 5σ upper limit on the average absolute escape fraction of <24%, consistent with similar studies. With future planned observations, the sample sizes should rapidly increase and the method presented here should provide very robust constraints on the escape fraction.

  • 14. Atek, H.
    et al.
    Kunth, D.
    Schaerer, D.
    Hayes, M.
    Deharveng, J. M.
    Östlin, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mas-Hesse, J. M.
    Empirical estimate of Lyα escape fraction in a statistical sample of Lyα emitters2009In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 506, no 2, p. L1-L4Article in journal (Refereed)
    Abstract [en]

    Context: The Lyman-alpha (Lyα) recombination line is a fundamental tool for galaxy evolution studies and modern observational cosmology. However, subsequent interpretations are still prone to a number of uncertainties. Besides numerical efforts, empirical data are urgently needed for a better understanding of the Lyα escape process. Aims: We empirically estimate the Lyα escape fraction in a statistically significant sample of galaxies in a redshift range z ~ 0 - 0.3. This estimate will constrain interpretations of current high-redshift Lyα observations. Methods: An optical spectroscopic follow-up of a sub-sample of 24 Lyα emitters detected by GALEX at z ~ 0.2 - 0.3, combined with a UV-optical sample of local starbursts, both with matched apertures, allow us to quantify the dust extinction through Balmer lines, and to estimate the Lyα escape fraction from the Hα flux corrected for extinction in the framework of the recombination theory. Results: The global escape fraction of Lyα radiation spans a wide range of values and fesc(Lyα) clearly decreases with increasing nebular dust extinction E(B-V). Several objects show fesc(Lyα) greater than fesc(continuum), which may be taken as observational evidence for a clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture size effects may still prevail between z ~ 0.2 - 0.3 Lyman-alpha emitters (LAEs) and local starbursts and may explain the difference observed for fesc(Lyα).

  • 15. Atek, Hakim
    et al.
    Kunth, Daniel
    Hayes, Matthew
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mas-Hesse, J. M.
    On the detectability of Ly-alpha emission in star forming galaxies. The role of dust2008In: Astronomy and Astrophysics, Vol. 488, no 491Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Context: Lyman-alpha (Lyα) radiation is now widely used to investigate the galaxy formation and evolution in the high redshift universe. However, without a rigorous understanding of the processes regulating the Lyα escape fraction, physical interpretations of high-z observations remain questionable. Aims: We examine six nearby star forming galaxies to disentangle the role of the dust from other parameters such as gas kinematics, geometry, and ISM morphology in the obscuration of Lyα. Thereby, we attempt to understand the Lyα escape physics and infer the implications for high-redshift studies. Methods: We use HST/ACS imaging to produce continuum-subtracted Lyα maps, and ground-based observations (ESO/NTT and NOT) to map the Hα emission and the extinction E(B-V) in the gas phase derived from the Balmer decrement Hα/Hβ. Results: When large outflows are present, the Lyα emission does not appear to be correlated with the dust content, confirming the role of the Hi kinematics in the escape of Lyα photons. In the case of a dense, static Hi covering, we observe a damped absorption with a negative correlation between Lyα and E(B-V). We found that the Lyα escape fraction does not exceed 10% in all our galaxies and is mostly about 3% or below. Finally, because of the radiative transfer complexity of the Lyα line, star formation rate based on Lyα luminosity is underestimated with respect to that derived from UV luminosity. Simple reddening correction does not reconcile SFR(Lyα) with the total star formation rate. Conclusions: The dust is not necessarily the main Lyα escape regulatory factor. ISM kinematics and geometry may play a more significant role. The failure of simple dust correction to recover the intrinsic Lyα/Hα ratio or the total star formation rate should prompt us to be more cautious when interpreting high-z observations and related properties, such as SFRs based on Lyα alone. To this end, we propose a more realistic calibration for SFR(Lyα), which accounts for dust attenuation and resonant scattering effects via the Lyα escape fraction.

  • 16. Atek, Hakim
    et al.
    Kunth, Darnel
    Schaerer, Darnel
    Mas-Hesse, J. Miguel
    Hayes, Matthew
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kneib, Jean-Paul
    Influence of physical galaxy properties on Ly alpha escape in star-forming galaxies2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 561, p. A89-Article in journal (Refereed)
    Abstract [en]

    Context. Among the different observational techniques used to select high-redshift galaxies, the hydrogen recombination line Lyman-alpha (Ly alpha) is of particular interest because it gives access to the measurement of cosmological quantities such as the star formation rate (SFR) of distant galaxy populations. However, interpreting this line and calibrating such observables are still subject to serious uncertainties. Aims. In this context, it important to understand the mechanisms responsible for the attenuation of Ly alpha emission, and under what conditions the Ly alpha emission line can be used as a reliable star formation diagnostic tool. Methods. We used a sample of 24 Ly alpha emitters at z similar to 0.3 with an optical spectroscopic follow-up to calculate the Ly alpha escape fraction and its dependence upon different physical properties. We also examined the reliability of Ly alpha as a SFR indicator. We combined these observations with a compilation of Ly alpha emitters selected at z = 0-0.3 from the literature to assemble a larger sample. Results. We confirm that the Ly alpha escape fraction clearly depends on the dust extinction following the relation f(esc)(Ly alpha) = C-Ly alpha x 10(-0.4 E(B-V) kLy alpha) where k(Ly alpha) similar to 6.67 and C-Ly alpha = 0.22. However, the correlation does not follow the expected curve for a simple dust attenuation. A higher attenuation can be attributed to a scattering process, while f(esc)(Ly alpha) values that are clearly above the continuum extinction curve can be the result of various mechanisms that can lead to an enhancement of the Ly alpha output. We also observe that the strength of Ly alpha and the escape fraction appear unrelated to the galaxy metallicity. Regarding the reliability of Ly alpha as a SFR indicator, we show that the deviation of SFR(Ly alpha) from the true SFR (as traced by the UV continuum) is a function of the observed SFR(UV), which can be seen as the decrease in f(esc)(Ly alpha) with increasing UV luminosity. Moreover, we observe redshift dependence of this relationship, revealing the underlying evolution of f(esc)(Ly alpha) with redshift.

  • 17. Bergvall, Nils
    et al.
    Marquart, Thomas
    Way, Michael J.
    Blomqvist, Anna
    Holst, Emma
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Local starburst galaxies and their descendants Statistics from the Sloan Digital Sky Survey2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A72Article in journal (Refereed)
    Abstract [en]

    Aims. Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies.

    Methods. Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H alpha line. These masses agree excellently with the photometric masses. The mass (gas + stars) range is similar to 10(9)-10(11.5) M-circle dot. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/< SFR >, requiring that b >= 3. For postburst galaxies, we use, the equivalent width of H delta in absorption with the criterion EWH delta,abs >= 6 angstrom.

    Results. We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3 6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages similar to 10 Myr, while almost no starbursts are found at ages >1 Gyr. The median baryonic burst mass fraction of sub-L* galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions >3%) is bimodal with a break at log M (M-circle dot) similar to 10.6, above which the ages are doubled. The starburst and postburst luminosity functions (LFs) follow each other closely until M-r similar to -21, when active galactic nuclei (AGNs) begin to dominate. The postburst LF continues to follow the AGN LF, while starbursts become less significant. This suggests that the number of luminous starbursts is underestimated by about one dex at high luminosities, because of having large amounts of dust and/or being outshone by an AGN. It also indicates that the starburst phase preceded the AGN phase. Finally, we look at the conditions for global gas outflow caused by stellar feedback and find that massive starburst galaxies are susceptible to such outflows.

  • 18. Bergvall, Nils
    et al.
    Zackrisson, Erik
    Andersson, B.-G.
    Arneberg, D.
    Masegosa, J.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    First detection of Lyman continuum escape from a local starburst galaxy. I. Observations of the luminous blue compact galaxy Haro 11 with the Far Ultraviolet Spectroscopic Explorer (FUSE)2006In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 448, no 2, p. 513-524Article in journal (Refereed)
    Abstract [en]

    Context: The dominating reionization source in the young universe has not yet been identified. Possible candidates include metal poor dwarf galaxies with starburst properties.

    Aims. We selected an extreme starburst dwarf, the Blue Compact Galaxy Haro 11, with the aim of determining the Lyman continuum escape fraction from UV spectroscopy.

    Methods. Spectra of Haro 11 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, these data correspond to a hydrogen column density of ~10^19cm^-2. This relatively high value indicates that most of the LyC photons escape through transparent holes in the interstellar medium. We then use spectral evolutionary models to constrain the escape fraction of the produced LyC photons.

    Results. Assuming a normal Salpeter initial mass function we obtain a Lyman continuum escape fraction of f_esc˜ 4-10%. We argue that in a hierarchical galaxy formation scenario, the upper limit we derive for the escape rate allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

  • 19.
    Bik, Adrianus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hayes, Matthew
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Amram, P.
    VLT/MUSE view of the highly ionized outflow cones in the nearby starburst ESO338-IG042015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 576, article id L13Article in journal (Refereed)
    Abstract [en]

    Context. The Lya line is an important diagnostic for star formation at high redshift, but interpreting its flux and line profile is difficult because of the resonance nature of Lya. Trends between the escape of Lya photons and dust and properties of the interstellar medium (ISM) have been found, but detailed comparisons between Lya emission and the properties of the gas in local high-redshift analogs are vital for understanding the relation between Lya emission and galaxy properties. Aims. For the first time, we can directly infer the properties of the ionized gas at the same location and similar spatial scales of the extended Lya halo around the local Lya emitter and Lyman-break galaxy analog ESO338-IG04. Methods. We obtained VLT/MUSE integral field spectra. We used ionization parameter mapping of the [S II]/[O III] line ratio and the kinematics of Ha to study the ionization state and kinematics of the ISM of ESO 338-IG04. Results. The velocity map reveals two outflows, one toward the north, the other toward the south of ESO338. The ionization parameter mapping shows that the entire central area of the galaxy is highly ionized by photons leaking from the HII regions around the youngest star clusters. Three highly ionized cones have been identified, of which one is associated with an outflow detected in the Ha. We propose a scenario where the outflows are created by mechanical feedback of the older clusters, while the highly ionized gas is caused by the hard ionizing photons emitted by the youngest clusters. A comparison with the Lya map shows that the (approximately bipolar) asymmetries observed in the Lya emission are consistent with the base of the outflows detected in Ha. No clear correlation with the ionization cones is found. Conclusions. The mechanical and ionization feedback of star clusters significantly changes the state of the ISM by creating ionized cones and outflows. The comparison with Lya suggests that especially the outflows could facilitate the escape of Lya photons.

  • 20.
    Blasco-Herrera, J.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Font, J.
    Beckman, J. E.
    H alpha kinematics of 11 starburst galaxies selected from the Sloan Digital Sky Survey2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 435, no 3, p. 1958-1983Article in journal (Refereed)
    Abstract [en]

    We present analysis of Fabry-Perot interferometric observations for a sample of 11 starburst galaxies with redshift z less than or similar to 0.03 selected from the Sloan Digital Sky Survey. We have targeted the H alpha lambda 6562.78 emission line at spatial sampling of 0.2arcsec-0.4 arcsec and at spectral resolution of R similar to 16 000. Studying two-dimensional maps for the velocity, velocity dispersion, line emission and continuum deliver new insights into the nature of starburst and postburst galaxies. The velocity fields are fitted to an exponential disc model, providing scalelengths and masses, to be compared with the photometric scalelength and the mass estimated from the velocity dispersions. From the line emission, the star formation rates are also calculated and compared with values in the literature. We have found that between 55 and 64 per cent of our sample show large-scale dominating rotation, while 27 per cent show local rotation typically restricted to the central part of each system. The morphology and line profiles in the centre of eight objects are consistent with a recent merger, while another two seem to be involved in a accretion process which, for the moment, has not disrupted their kinematics.

  • 21.
    Blasco-Herrera, Javier
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Physics, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Beckman, J.
    Gutierrez, L.
    Lundgren, A.
    Epinat, B.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Physics, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Font, J.
    Hernandez, O.
    de Denus-Baillargeon, M. -M
    Carignan, C.
    An improved method for statistical studies of the internal kinematics of H ii regions: the case of M832010In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 407, no 4, p. 2519-2529Article in journal (Refereed)
    Abstract [en]

    We present the integrated H alpha emission line profile for 157 H ii regions in the central 3.4 x 3.4 arcmin2 of the galaxy M83 (NGC 5236). Using the Fabry-Perot interferometer GH alpha FaS, on the 4.2-m William Herschel Telescope on La Palma, we show the importance of a good characterization of the instrumental response function for the study of line profile shapes. The luminosity-velocity dispersion relation is also studied, and in the log(L)-log(Sigma) plane we do not find a linear relation, but an upper envelope with equation log(L-H alpha) = 0.9 log(Sigma) + 38.1. For the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity L = 1038.5 erg s-1, in full agreement with previous studies of other galaxies, reinforcing the idea of using H ii regions as standard candles.

  • 22.
    Blasco-Herrera, Javier
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Font, J.
    Instituto de Astrof´ısica de Canarias, Tenerife, Spain.
    Beckman, J .E.
    Instituto de Astrof´ısica de Canarias, Tenerife, Spain.
    Halpha kinematics of 11 starburst galaxies selected from the Sloan Digital Sky Survey2012Manuscript (preprint) (Other academic)
    Abstract [en]

    We present analysis of Fabry-Perot interferometric observations for a sample of 11starburst galaxies with redshift z . 0.03 selected from the Sloan Digital Sky Survey.We have targeted the H 6562.78 emission line at spatial sampling of 0.002−0.004 andat spectral resolution of R 16000, and studying two-dimensional velocity, velocitydispersion, line emission and continuum maps deliver new insights into the nature ofstarburst and postburst galaxies. The velocity fields are fitted to an exponential discmodel, providing scale lengths and masses, to be compared with the photometric scalelength and the mass estimated from the velocity dispersions. From the line emissionthe star formation rates are also calculated and compared with values in the literature.We have found that between 55% and 64% of our sample show large scale dominatingrotation, while 27% show local rotation typically restricted to the central part of eachsystem. The morphology and line profiles in the centre of eight objects are consistentwith a recent merger, while another two seem to be involved in a accretion processwhich has not disrupted their kin

  • 23.
    Blasco-Herrera, Javier
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bergvall, N.
    Department of Physics and Astronomy, Uppsala University, Sweden.
    Marquart, T.
    Department of Physics and Astronomy, Uppsala University, Sweden.
    Structural parameters of starburst and postburst galaxies2012Manuscript (preprint) (Other academic)
    Abstract [en]

    We present two samples of 1173 starbursts and 145 postburst in the redshift range0.01 < z < 0.083, selected from Sloan Digital Sky Survey Data Release 7. We charac-terize both samples using 2D Sersic profiles and measure their asymmetry. The Sersicindex, n, and the effective radii show that starburst galaxies are more concentratedthan the postburst sample, with median n 1.85 for starbursts and 2.85 for post-bursts. There is a large fraction of disky (n < 2) postbursts, a fraction larger thanreported by previous studies. Part of the excess comes from low luminosity (Mr > −19)objects, vastly dominated by discs. We estimate the mass from the velocity dispersionof the H emission line, both for the starbursts and those postbursts with residualemission, finding that Lr / Mb, with b = 1.35 for starbursts and b = 1.5 for post-bursts. The typical values of the mass-to-light ratio range between 0 and 10. This,now, is surprising for starburst galaxies, for which mass-to-light ratios 1 have beenpreviously found.

  • 24.
    Bridge, Joanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Pennsylvania State University, USA; University of Louisville, USA.
    Hayes, Matthew
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gronwall, Caryl
    Ciardullo, Robin
    Atek, Hakim
    Cannon, John M.
    Gronke, Max
    Guaita, Lucia
    Hagen, Alex
    Herenz, Edmund Christian
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kunth, Daniel
    Laursen, Peter
    Miguel Mas-Hesse, J.
    Pardy, Stephen A.
    The Ly alpha Reference Sample. VIII. Characterizing Ly alpha Scattering in Nearby Galaxies2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 852, no 1, article id 9Article in journal (Refereed)
    Abstract [en]

    We examine the dust geometry and Ly alpha scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < z < 0.2) Ly alpha-emitting and starbursting systems with Hubble Space Telescope Ly alpha, H alpha, and H beta imaging. We find that the global dust properties determined by line ratios are consistent with other studies, with some of the LARS galaxies exhibiting clumpy dust media, while others of them show significantly lower Ly alpha emission compared to their Balmer decrement. With the LARS imaging, we present Ly alpha/H alpha and H alpha/H beta maps with spatial resolutions as low as similar to 40 pc, and use these data to show that in most galaxies, the dust geometry is best modeled by three distinct regions: a central core where dust acts as a screen, an annulus where dust is distributed in clumps, and an outer envelope where Ly alpha photons only scatter. We show that the dust that affects the escape of Ly alpha is more restricted to the galaxies' central regions, while the larger Ly alpha halos are generated by scattering at large radii. We present an empirical modeling technique to quantify how much Ly alpha scatters in the halo, and find that this characteristic scattering distance correlates with the measured size of the Ly alpha halo. We note that there exists a slight anti-correlation between the scattering distance of Ly alpha and global dust properties.

  • 25. Calzetti, D.
    et al.
    Johnson, K. E.
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gallagher, J. S.
    Andrews, J. E.
    Smith, L. J.
    Clayton, G. C.
    Lee, J. C.
    Sabbi, E.
    Ubeda, L.
    Kim, H.
    Ryon, J. E.
    Thilker, D.
    Bright, S. N.
    Zackrisson, E.
    Kennicutt, R. C.
    de Mink, S. E.
    Whitmore, B. C.
    Aloisi, A.
    Chandar, R.
    Cignoni, M.
    Cook, D.
    Dale, D. A.
    Elmegreen, B. G.
    Elmegreen, D. M.
    Evans, A. S.
    Fumagalli, M.
    Gouliermis, D. A.
    Grasha, K.
    Grebel, E. K.
    Krumholz, M. R.
    Walterbos, R.
    Wofford, A.
    Brown, T. M.
    Christian, C.
    Dobbs, C.
    Herrero, A.
    Kahre, L.
    Messa, Matteo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nair, P.
    Nota, A.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pellerin, A.
    Sacchi, E.
    Schaerer, D.
    Tosi, M.
    THE BRIGHTEST YOUNG STAR CLUSTERS IN NGC 52532015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 811, no 2, article id 75Article in journal (Refereed)
    Abstract [en]

    The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the radio nebula). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 angstrom 1.9 mu m in 13 filters. These include H alpha, P beta, and P alpha, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (M-V < -8.8) and the two young radio nebula clusters. The clusters have ages similar to 1-15 Myr and masses similar to 1 x 10(4)-2.5 x 10(5) M-circle dot. The clusters' spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last similar to 15 Myr. The most massive cluster is in the radio nebula; with a mass similar to 2.5 x 10(5) M-circle dot and an age similar to 1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV similar to 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also similar to 1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.

  • 26. Calzetti, D.
    et al.
    Lee, J. C.
    Sabbi, E.
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy.
    Smith, L. J.
    Andrews, J. E.
    Ubeda, L.
    Bright, S. N.
    Thilker, D.
    Aloisi, A.
    Brown, T. M.
    Chandar, R.
    Christian, C.
    Cignoni, M.
    Clayton, G. C.
    da Silva, R.
    de Mink, S. E.
    Dobbs, C.
    Elmegreen, B. G.
    Elmegreen, D. M.
    Evans, A. S.
    Fumagalli, M.
    Gallagher, J. S. , I I I
    Gouliermis, D. A.
    Grebel, E. K.
    Herrero, A.
    Hunter, D. A.
    Johnson, K. E.
    Kennicutt, R. C.
    Kim, H.
    Krumholz, M. R.
    Lennon, D.
    Levay, K.
    Martin, C.
    Nair, P.
    Nota, A.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pellerin, A.
    Prieto, J.
    Regan, M. W.
    Ryon, J. E.
    Schaerer, D.
    Schiminovich, D.
    Tosi, M.
    Van Dyk, S. D.
    Walterbos, R.
    Whitmore, B. C.
    Wofford, A.
    LEGACY EXTRAGALACTIC UV SURVEY (LEGUS) WITH THE HUBBLE SPACE TELESCOPE. I. SURVEY DESCRIPTION2015In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 149, no 2, article id 51Article in journal (Refereed)
    Abstract [en]

    The Legacy ExtraGalactic UV Survey (LEGUS) is a Cycle 21 Treasury program on the Hubble Space Telescope aimed at the investigation of star formation and its relation with galactic environment in nearby galaxies, from the scales of individual stars to those of similar to kiloparsec-size clustered structures. Five-band imaging from the nearultraviolet to the I band with the Wide-Field Camera 3 (WFC3), plus parallel optical imaging with the Advanced Camera for Surveys (ACS), is being collected for selected pointings of 50 galaxies within the local 12 Mpc. The filters used for the observations with the WFC3 are F275W(lambda 2704 angstrom), F336W(lambda 3355 angstrom), F438W(lambda 4325 angstrom), F555W(lambda 5308 angstrom), and F814W(lambda 8024 angstrom); the parallel observations with the ACS use the filters F435W (lambda 4328 angstrom), F606W(lambda 5921 angstrom), and F814W(lambda 8057 angstrom). The multiband images are yielding accurate recent (less than or similar to 50 Myr) star formation histories from resolved massive stars and the extinction-corrected ages and masses of star clusters and associations. The extensive inventories of massive stars and clustered systems will be used to investigate the spatial and temporal evolution of star formation within galaxies. This will, in turn, inform theories of galaxy evolution and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of star formation at high redshift. This paper describes the survey, its goals and observational strategy, and the initial scientific results. Because LEGUS will provide a reference survey and a foundation for future observations with the James Webb Space Telescope and with ALMA, a large number of data products are planned for delivery to the community.

  • 27. Calzetti, D.
    et al.
    Wilson, G. W.
    Draine, B. T.
    Roussel, H.
    Johnson, K. E.
    Heyer, M. H.
    Wall, W. F.
    Grasha, K.
    Battisti, A.
    Andrews, J. E.
    Kirkpatrick, A.
    González, D. Rosa
    Vega, O.
    Puschnig, Johannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yun, M.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Evans, A. S.
    Tang, Y.
    Lowenthal, J.
    Sánchez-Arguelles, D.
    Spatially Resolved Dust, Gas, and Star Formation in the Dwarf Magellanic Irregular NGC 44492018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 852, no 2, article id 106Article in journal (Refereed)
    Abstract [en]

    We investigate the relation between gas and star formation in subgalactic regions, similar to 360. pc to similar to 1.5. kpc in size, within the nearby starburst dwarf NGC 4449, in order to separate the underlying relation from the effects of sampling at varying spatial scales. Dust and gas mass surface densities are derived by combining new observations at 1.1. mm, obtained with the AzTEC instrument on the Large Millimeter Telescope, with archival infrared images in the range 8-500 mu m from the Spitzer Space Telescope and the Herschel Space Observatory. We extend the dynamic range of our millimeter (and dust) maps at the faint end, using a correlation between the far-infrared/millimeter colors F(70)/F(1100) (and F(160)/F(1100)) and the mid-infrared color F(8)/F(24) that we establish for the first time for this and other galaxies. Supplementing our data with maps of the extinction-corrected star formation rate (SFR) surface density, we measure both the SFR-molecular gas and the SFR-total. gas relations in NGC 4449. We find that the SFR-molecular. gas relation is described by a power law with an exponent that decreases from similar to 1.5 to similar to 1.2 for increasing region size, while the exponent of the SFR-total. gas relation remains constant with a value of similar to 1.5 independent of region size. We attribute the molecular law behavior to the increasingly better sampling of the molecular cloud mass function at larger region sizes; conversely, the total gas law behavior likely results from the balance between the atomic and molecular gas phases achieved in regions of active star formation. Our results indicate a nonlinear relation between SFR and gas surface density in NGC 4449, similar to what is observed for galaxy samples.

  • 28.
    Cumming, Robert
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Stellar dynamics of blue compact galaxies. II. Further indications of a merger in ESO 338-IG042007Report (Other academic)
    Abstract [en]

    Luminous blue compact galaxies, common at z~1 but now relatively rare, show disturbed kinematics in emission lines. As part of a programme to understand their formation and evolution, we have investigated the stellar dynamics of a number of nearby objects in this class. We obtained long-slit spectra with VLT/FORS2 in the spectral region covering the near-infrared calcium triplet. In this paper we focus on the well-known luminous blue compact galaxy ESO 338-IG04 (Tololo 1924-416). A previous investigation, using Fabry-Perot interferometry, showed that this galaxy has a chaotic H-alpha velocity field, indicating that either the galaxy is not in dynamical equilibrium or that H-alpha does not trace the gravitational potential due to feedback from star formation. Along the apparent major axis, the stellar and ionised gas velocities for the most part follow each other. The chaotic velocity field must therefore be a sign that the young stellar population in ESO 338-IG04 is not in dynamical equilibrium. The most likely explanation, which is also supported by its morphology, is that the galaxy has experienced a merger and that this has triggered the current starburst. Summarising the results of our programme so far, we note that emission-line velocity fields are not always reliable tracers of stellar motions, and go on to assess the implications for kinematic studies of similar galaxies at intermediate redshift.

  • 29.
    Cumming, Robert J.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Marquart, Thomas
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Bergvall, Nils
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy.
    Stellar kinematics in blue compact galaxies2009Other (Other (popular science, discussion, etc.))
    Abstract [en]

    In a programme of observations of local luminous blue compact galaxies (BCGs), we are investigating kinematics by using tracers of both stars and ionized gas. Here we summarise our program and present new data on the local Lyman break galaxy analogue Haro 11. From spatially-resolved spectroscopy around the near-infrared Ca II triplet, we find that its stars and ionized gas have similar velocity fields. Our programme so far indicates however that emission line velocities can differ locally by a few tens of km/s from the Ca II values. Comparing our data to simple stellar population models, we assess which stellar population the Ca II triplet traces and its potential beyond the local universe.

  • 30.
    Cumming, Robert James
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Marquart, Thomas
    Masegosa, Josefa
    Bergvall, Nils
    Amram, Philippe
    Stellar dynamics of blue compact galaxies.: II. Further indications of a merger in ESO 338-IG042008In: Astronomy & Astrophysics, Vol. 479, no 3Article in journal (Refereed)
    Abstract [en]

    Context: Luminous blue compact galaxies, common at z ~ 1 but now relatively rare, show disturbed kinematics in emission lines. Aims: As part of a programme to understand their formation and evolution, we have investigated the stellar dynamics of a number of nearby objects in this class. Methods: We obtained long-slit spectra with VLT/FORS2 in the spectral region covering the near-infrared calcium triplet. In this paper we focus on the well-known luminous blue compact galaxy ESO 338-IG04 (Tololo 1924-416). A previous investigation, using Fabry-Perot interferometry, showed that this galaxy has a chaotic Hα velocity field, indicating that either the galaxy is not in dynamical equilibrium or that Hα does not trace the gravitational potential due to feedback from star formation. Results: Along the apparent major axis, the stellar and ionised gas velocities for the most part follow each other. The chaotic velocity field must therefore be a sign that the young stellar population in ESO 338-IG04 is not in dynamical equilibrium. The most likely explanation, which is also supported by its morphology, is that the galaxy has experienced a merger and that this has triggered the current starburst. Summarising the results of our programme so far, we note that emission-line velocity fields are not always reliable tracers of stellar motions, and go on to assess the implications for kinematic studies of similar galaxies at intermediate redshift.

  • 31.
    Cumming, Robert
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Marquart, Thomas
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergvall, Nils
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy.
    Stellar kinematics in blue compact galaxies2009Report (Other academic)
    Abstract [en]

    In a programme of observations of local luminous blue compact galaxies (BCGs), we are investigating kinematics by using tracers of both stars and ionized gas. Here we summarise our program and present new data on the local Lyman break galaxy analogue Haro 11. From spatially-resolved spectroscopy around the near-infrared Ca II triplet, we find that its stars and ionized gas have similar velocity fields. Our programme so far indicates however that emission line velocities can differ locally by a few tens of km/s from the Ca II values. Comparing our data to simple stellar population models, we assess which stellar population the Ca II triplet traces and its potential beyond the local universe.

  • 32. Dahlen, Tomas
    et al.
    Melinder, J.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mencia Trinchant, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, S.
    Ostlin, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    The Stockholm Vimos Supernova Survey (SVISS) - First Results From An Intermediate Redshift Sn Survey2009Conference paper (Refereed)
    Abstract [en]

    The aim of the Stockholm VIMOS Supernova Survey is to find and characterize supernovae in the redshift range 0.1 to 1.2 and to derive accurate supernova rate densities for this redshift range. A preliminary analysis show that we have 14 prime SN candidates and an additional 23 less secure detections in one of our search fields. A sample of R+I light curves for the prime candidates will be presented. We will also show some results from testing of our supernova search pipeline and our supernova typing method.

  • 33. de Grijs, Richard
    et al.
    Anders, Peter
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The NGC 5253 star cluster system - I. Standard modelling and infrared-excess sources2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 431, no 3, p. 2917-2932Article in journal (Refereed)
    Abstract [en]

    Using high-resolution Hubble Space Telescope data, we re-examine the fundamental properties (ages, masses and extinction values) of the rich star cluster population in the dwarf starburst galaxy NGC 5253. The gain in resolution compared to previous studies is of order a factor of 2 in both spatial dimensions, while our accessible wavelength range transcends previous studies by incorporation of both near-ultraviolet and near-infrared (IR) passbands. We apply spectral synthesis treatments based on two different simple stellar population model suites to our set of medium-, broad-band and H alpha images to gain an improved physical understanding of the IR-excess flux found for a subset of young clusters (30 of 149). With the caveat that our models are based on fully sampled stellar mass functions, the NGC 5253 cluster population is dominated by a significant number of relatively low-mass (M-cl less than or similar to a few x 10(4) M-circle dot) objects with ages ranging from a few x 10(6) to a few x 10(7) yr, which is in excellent agreement with the starburst age of the host galaxy. The IR-excess clusters are almost all found in this young age range and have masses of up to a few x 10(4) M-circle dot. The IR excess in the relatively low-mass NGC 5253 clusters is most likely caused by a combination of stochastic sampling effects and colour variations due to the presence of either luminous red or pre-main-sequence stars. We also find a small number of intermediate-age (similar to 1 Gyr old), similar to 10(5) M-circle dot clusters, as well as up to a dozen massive, similar to 10 Gyr old globular clusters. Their presence supports the notion that NGC 5253 is a very active galaxy that has undergone multiple episodes of star cluster formation.

  • 34.
    Duval, Florent
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schaerer, D.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Laursen, P.
    Lyman alpha line and continuum radiative transfer in a clumpy interstellar medium2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. A52-Article in journal (Refereed)
    Abstract [en]

    Aims. We study the effects of an inhomogeneous interstellar medium (ISM) on the strength and the shape of the Lyman alpha (Ly alpha) line in starburst galaxies. Methods. Using our 3D Monte Carlo Ly alpha radiation transfer code, we have studied the radiative transfer of Ly alpha, UV, and optical continuum photons in homogeneous and clumpy shells of neutral hydrogen and dust surrounding a central source. Our simulations predict the Ly alpha and continuum escape fraction, the Ly alpha equivalent width EW(Ly alpha), the Ly alpha line profile, and their dependence on the geometry of the gas distribution and the main input physical parameters. Results. The ISM clumpiness is found to have a strong impact on the Ly alpha line radiative transfer, leading to a strong dependence of the emergent features of the Ly alpha line (escape fraction, EW(Ly alpha)) on the ISM morphology. Although a clumpy and dusty ISM appears more transparent to radiation (both line and continuum) compared to an equivalent homogeneous ISM of equal dust optical depth, we find that the Ly alpha photons are, in general, still more attenuated than UV continuum radiation. As a consequence, the observed equivalent width of the Ly alpha line (EWobs(Ly alpha)) is lower than the intrinsic one (EWint(Ly alpha)) for nearly all clumpy ISM configurations being considered. There are, however, special conditions under which Ly alpha photons escape more easily than the continuum, resulting in an enhanced EWobs(Ly alpha). The requirement for this to happen is that the ISM is almost static (galactic outflows <= 200 km s(-1)), extremely clumpy (with density contrasts >10(7) in HI between clumps and the interclump medium), and very dusty (E(B - V) > 0.30). When these conditions are fulfilled, the emergent Ly alpha line profile generally shows no velocity shift and little asymmetry. Otherwise, the Ly alpha line profile is very similar to the one expected for homogeneous media. Conclusions. Given the asymmetry and velocity shifts generally observed in star-forming galaxies with Ly alpha emission, we therefore conclude that clumping is unlikely to significantly enhance their relative Ly alpha/UV transmission.

  • 35.
    Duval, Florent
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hayes, Matthew
    Stockholm University, Faculty of Science, Department of Astronomy.
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zackrisson, Erik
    Stockholm University, Faculty of Science, Department of Astronomy.
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy.
    Guaita, L.
    Rivera-Thorsen, Thöger
    Stockholm University, Faculty of Science, Department of Astronomy.
    Verhamme, A.
    Orlitova, I.
    Schaerer, D.
    Herenz, E. C.
    Gruyters, P.
    Mansson, T.
    LARS VIII: Lyman alpha escape from the edge-on disk galaxy Mrk1486In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 36.
    Duval, Florent
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). The University of Tokyo, Japan.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hayes, Matthew
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zackrisson, Erik
    Verhamme, Anne
    Orlitova, Ivana
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). INAF Observatorio Astronomico di Roma, Italy.
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cannon, John M.
    Laursen, Peter
    Rivera-Thorsen, Thöger
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Herenz, E. Christian
    Gruyters, Pieter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Miguel Mas-Hesse, J.
    Kunth, Daniel
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schaerer, Daniel
    Månsson, Tore
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The Lyman alpha reference sample VI. Lyman alpha escape from the edge-on disk galaxy Mrk 14862016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A77Article in journal (Refereed)
    Abstract [en]

    Context. Recent numerical simulations suggest that the strength of the Lyman alpha (Ly alpha) line of star-forming disk galaxies strongly depends on the inclination at which they are observed: from edge-on to face-on, we expect to see a change from a strongly attenuated Ly alpha line to a strong Ly alpha emission line.

    Aims. We aim to understand how a strong Ly alpha emission line is able to escape from the low-redshift highly inclined (edge-on) disk galaxy Mrk 1486 (z similar to 0.0338). To our knowledge, this work is the first observational study of Ly alpha transport inside an edge-on disk galaxy.

    Methods. Using a large set of HST imaging and spectroscopic data, we investigated the interstellar medium (ISM) structure and the dominant source of Ly alpha radiation inside Mrk 1486. Moreover, using a 3D Monte Carlo Ly alpha radiation transfer code, we studied the radiative transfer of Ly alpha and UV continuum photons inside a 3D geometry of neutral hydrogen (HI) and dust that models the ISM structure at the galaxy center. Our numerical simulations predicted the Ly alpha line profile that we then compared to the one observed in the HST/COS spectrum of Mrk 1486.

    Results. While a pronounced Ly alpha absorption line emerges from the disk of Mrk 1486, very extended Ly alpha structures are observed at large radii from the galaxy center: a large Ly alpha-halo and two very bright Ly alpha regions located slightly above and below the disk plane. The analysis of IFU H alpha spectroscopic data of Mrk 1486 indicates the presence of two bipolar outflowing halos of HI gas at the same location as these two bright Ly alpha regions. Comparing different diagnostic diagrams (such as [OIII](5007)/H beta versus [OI](6300)/H alpha) to photo-and shock-ionization models, we find that the Ly alpha production of Mrk 1486 is dominated by photoionization inside the galaxy disk. From this perspective, our numerical simulations succeed in reproducing the strength and shape of the observed Ly alpha emission line of Mrk 1486 by assuming a scenario in which the Ly alpha photons are produced inside the galaxy disk, travel along the outflowing halos, and scatter on cool HI materials toward the observer.

    Conclusions. Extended bipolar galactic winds are frequently observed from star-forming disk galaxies. Given the advantage Ly alpha photons take of such outflowing HI materials to easily escape from Mrk 1486, this mechanism may explain the origin of strong Ly alpha emission lines frequently observed from highly inclined galaxies at high-redshift. This therefore challenges the robustness of the expected viewing-angle effect on the Ly alpha properties of star-forming disk galaxies.

  • 37.
    fathi, kambiz
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Beckman, John
    Zurita, Almudena
    Relano, Monica
    Knapen, Johan
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Carignan, Claude
    Structure and evolution of star-forming gas in late-type spiral galaxies2007In: Stellar Populations as Building Blocks of Galaxies, Proceedings: AU Symposium #241, 2007Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628. We investigate the role of the individual HII regions together with the large-scale gravitational mechanisms which govern star formation and overall evolution in spiral galaxies. Our kinematical analysis (reinforced by literature maps in HI and CO at lower angular resolution) enables us to verify the presence of an inner rapidly rotating inner disk-like component which we attribute to long term secular evolution of the large-scale spiral arms and oval structure. We find that gas is falling in from the outer parts towards the bluer central regions. This could be an early phase in the formation of a pseudo-bulge. We find signatures of radial motions caused by an m=2 perturbation, which are likely to be responsible for the inflow of material forming the circumnuclear ring and the rapidly rotating inner structure.

  • 38. Fynbo, J. P. U.
    et al.
    Laursen, P.
    Ledoux, C.
    Moller, P.
    Durgapal, A. K.
    Goldoni, P.
    Gullberg, B.
    Kaper, L.
    Maund, J.
    Noterdaeme, P.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Strandet, M. L.
    Toft, S.
    Vreeswijk, P. M.
    Zafar, T.
    Galaxy counterparts of metal-rich damped Ly alpha absorbers - I. The case of the z=2.35 DLA towards Q2222-09462010In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 408, no 4, p. 2128-2136Article in journal (Refereed)
    Abstract [en]

    We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Ly alpha absorbers (DLAs). Our rationale is that high-metallicity DLAs due to the luminosity-metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Ly alpha emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([O II], [O III], H beta and H alpha) fall in the near-infrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the z(abs) = 2.354 DLA towards the z = 2.926 quasar Q2222-0946. This DLA is amongst the most metal-rich z > 2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn II, Si II, Ni II, Mn II and Fe II of -0.46 +/- 0.07, -0.51 +/- 0.06, -0.85 +/- 0.06, -1.23 +/- 0.06 and -0.99 +/- 0.06, respectively. The galaxy is detected in the Ly alpha, [O III] lambda lambda 4959, 5007 and H alpha emission lines at an impact parameter of about 0.8 arcsec (6 kpc at z(abs) = 2.354). Based on the H alpha line, we infer a star formation rate of 10M(circle dot) yr(-1), which is a lower limit due to the possibility of slit loss. Compared to the recently determined H alpha luminosity function for z = 2.2 galaxies, the DLA-galaxy counterpart has a luminosity of L similar to 0.1L*(H alpha). The emission-line ratios are 4.0 (Ly alpha/H alpha) and 1.2 ([O III]/H alpha). In particular, the Ly alpha line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA are consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.

  • 39.
    Guaita, Lucia
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Francke, H.
    Gawiser, E.
    Bauer, F. E.
    Hayes, M.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Padilla, N.
    Magellan/MMIRS near-infrared multi-object spectroscopy of nebular emission from star-forming galaxies at 2 < z < 32013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 551, p. A93-Article in journal (Refereed)
    Abstract [en]

    Aims. To investigate the ingredients, which allow star-forming galaxies to present Ly alpha line in emission, we studied the kinematics and gas phase metallicity of the interstellar medium. Methods. We used multi-object near-infrared spectroscopy with Magellan/MMIRS to study nebular emission from z similar or equal to 2-3 star-forming galaxies discovered in three MUSYC fields. Results. We detected emission lines from four active galactic nuclei and 13 high-redshift star-forming galaxies, including H alpha lines down to a flux of (4 +/- 1)E-17 erg s(-1) cm(-2). This yielded seven new redshifts. The most common emission line detected is [OIII]5007, which is sensitive to metallicity. We were able to measure metallicity (Z) for two galaxies and to set upper (lower) limits for another two (two). The metallicity values are consistent with 0.3 < Z/Z(circle dot) < 1.2, 12 + log (O/H) similar to 8.2-8.8. Comparing the Ly alpha central wavelength with the systemic redshift, we find Delta(vLy alpha-[OIII]5007) = 70 270 km s(-1). Conclusions. High-redshift star-forming galaxies, Ly alpha emitting (LAE) galaxies, and H alpha emitters appear to be located in the low mass, high star-formation rate (SFR) region of the SFR versus stellar mass diagram, confirming that they are experiencing burst episodes of star formation, which are building up their stellar mass. Their metallicities are consistent with the relation found for z <= 2.2 galaxies in the Z versus stellar mass plane. The measured Delta(vLy alpha[OIII]5007) values imply that outflows of material, driven by star formation, could be present in the z similar to 2 3 LAEs of our sample. Comparing with the literature, we note that galaxies with lower metallicity than ours are also characterized by similar Delta(vLy alpha[OIII]5007) velocity off sets. Strong F([OIII]5007) is detected in many Ly alpha emitters. Therefore, we propose the F(Ly alpha)/F([OIII]5007) flux ratio as a tool for the study of high-redshift galaxies; while influenced by metallicity, ionization, and Ly alpha radiative transfer in the ISM, it may be possible to calibrate this ratio to primarily trace one of these effects.

  • 40.
    Guaita, Lucia
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hayes, Matthew
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gonzalez, Juan E.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Micheva, Genoveva
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Subaru Observatory, USA.
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mas-Hesse, J. M.
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Oti-Floranes, H.
    Schaerer, D.
    Verhamme, A.
    Freeland, Emily
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Orlitova, I.
    Laursen, P.
    Cannon, J. M.
    Duval, Florent
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rivera-Thorsen, Thøger
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Herenz, E. C.
    Kunth, D.
    Atek, H.
    Puschnig, Johannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gruyters, P.
    Pardy, S. A.
    The Lyman alpha reference sample IV. Morphology at low and high redshift2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 576, article id A51Article in journal (Refereed)
    Abstract [en]

    Context. The transport of Ly alpha photons in galaxies is a complex process and the conditions under which Ly alpha photons manage to escape from certain galaxies is still under investigation. The Lyman alpha reference sample (LARS) is a sample of 14 local star-forming galaxies, designed to study Ly alpha in detail and relate it to rest-frame UV and optical emission. Aims. With the aim of identifying rest-frame UV and optical properties, which are typical of Ly alpha emitters (LAEs, galaxies with EW(Ly alpha) > 20 angstrom) at both low and high redshift, we investigated the morphological properties of the LARS galaxies, in particular the ones that exhibit intense Ly alpha radiation. Methods. We measured sizes and morphological parameters in the continuum, Ly alpha, and Ha images. We studied morphology by using the Gini coefficient vs. M20 and asymmetry vs. concentration diagrams. We then simulated LARS galaxies at z similar to 2 and 5.7, performing the same morphological measurements. We also investigated the detectability of LARS galaxies in current deep field observations. The subsample of LAEs within LARS (LARS-LAEs) was stacked to provide a comparison to stacking studies performed at high redshift. Results. LARS galaxies have continuum size, stellar mass, and rest-frame absolute magnitude typical of Lyman break analogues in the local Universe and also similar to 2 < z < 3 star-forming galaxies and massive LAEs. LARS optical morphology is consistent with the one of merging systems, and irregular or starburst galaxies. For the first time we quantify the morphology in Ly alpha images: even if a variety of intrinsic conditions of the interstellar medium can favour the escape of Ly alpha photons, LARS-LAEs appear small in the continuum, and their Ly alpha is compact. LARS galaxies tend to be more extended in Ly alpha than in the rest-frame UV. It means that Ly alpha photons escape by forming haloes around HII regions of LARS galaxies. Conclusions. The stack of LARS-LAE Ly alpha images is peaked in the centre, indicating that the conditions, which make a galaxy an LAE, tend to produce a concentrated surface brightness profile. On the other hand, the stack of all LARS galaxies is shallower and more extended. This can be caused by the variety of dust and HI amount and distribution, which produces a more complex, patchy, and extended profile, like the one observed for Lyman break galaxies that can contribute to the stack. We cannot identify a single morphological property that controls whether a galaxy emits a net positive Ly alpha flux. However, the LARS-LAEs have continuum properties consistent with merging systems.

  • 41. Hayes, M.
    et al.
    Schaerer, D.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    The H-alpha luminosity function at redshift 2.2 A new determination using VLT/HAWK-I2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 509, no L5Article in journal (Refereed)
    Abstract [en]

    We aim to place new, strengthened constraints on the luminosity function (LF) of H-alpha (H alpha) emitting galaxies at redshift z approximate to 2.2, and to further constrain the instantaneous star-formation rate density of the universe ((rho) over dot(star)). We have used the new HAWK-I instrument at ESO-VLT to obtain extremely deep narrow-band (line; NB2090) and broad-band (continuum; K-s) imaging observations. The target field is in the GOODS-South, providing us with a rich multi-wavelength auxiliary data set, which we utilise for redshift confirmation and to estimate dust content. We use this new data to measure the faint-end slope (alpha) of LF(H alpha) with unprecedented precision. The data are well fit by a Schechter function and also a single power-law, yielding alpha = (-1.72 +/- 0.20) and (-1.77 +/- 0.21), respectively. Thus we are able to confirm the steepening of a from low-to high-z predicted by a number of authors and observed at other wavelengths. We combine our LF data-points with those from a much shallower but wider survey at z similar to 2.2 (Geach et al. 2008), constructing a LF spanning a factor of 50 in luminosity. Re-fitting the Schechter parameters, we obtain log L-star = (43.07 +/- 0.22) erg s(-1); log phi(star) = (-3.45 +/- 0.52) Mpc(-3); alpha = (-1.60 +/- 0.15). We integrate over LF(H alpha) and apply a correction for dust attenuation to determine the instantaneous cosmic star-formation rate density at z similar to 2 without assuming alpha or extrapolating it from lower-z. Our measurement of (rho) over dot(star) is (0.215 +/- 0.090) M-circle dot yr(-1) Mpc(-3), integrated over a range of 37 <= log(L-H alpha/erg s(-1)) <= 47.

  • 42.
    Hayes, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Scarlata, Claudia
    Lehnert, Matthew D.
    Mannerström-Jansson, Gustav
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    O VI EMISSION IMAGING OF A GALAXY WITH THE HUBBLE SPACE TELESCOPE: A WARM GAS HALO SURROUNDING THE INTENSE STARBURST SDSS J115630.63+500822.12016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 828, no 1, article id 49Article in journal (Refereed)
    Abstract [en]

    We report results from a new Hubble Space Telescope campaign that targets the O VI lambda lambda 1032, 1038 angstrom doublet in emission around intensely star-forming galaxies. The program aims to characterize the energy balance in starburst galaxies and gas cooling in the difficult-to-map coronal temperature regime of 2-5 x 10(5) K. We present the first resolved image of gas emission in the O VI line. Our target, SDSS J115630.63+500822.1, is very compact in the continuum but displays O VI emission to radii of 23 kpc. The surface brightness profile is well fit by an exponential with a scale length of 7.5 kpc. This is 10 times the size of the photoionized gas, and we estimate that about 1/6 the total O VI luminosity comes from resonantly scattered continuum radiation. Spectroscopy-which closely resembles a stacked sample of archival spectra-confirms the O VI emission, and determines the column density and outflow velocity from blueshifted absorption. The combination of measurements enables a large number of calculations with few assumptions. The O VI regions fill only similar to 10-3 of the volume. By comparing the cooling time with the cloud sound-crossing time, the cooling distance with the size, and the pressure in the O VI and nebular gas, we conclude that the O VI-bearing gas cannot have been lifted to the scale height at this temperature, and must be cooling in situ through this coronal temperature regime. The coronal phase contains similar to 1% of the ionized mass, and its kinetic energy at a given instant is similar to 1% of the budget set by supernova feedback. However, a much larger amount of the gas must have cooled through this phase during the star formation episode. The outflow exceeds the escape velocity and the gas may become unbound, but it will recombine before it escapes and become visible to Lyman (and O I) spectroscopy. The mapping of this gas represents a crucial step in further constraining galaxy formation scenarios and guiding the development of future astronomical satellites.

  • 43. Hayes, Matthew
    et al.
    Schaerer, Daniel
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mas-Hesse, J. Miguel
    Atek, Hakim
    Kunth, Daniel
    ON THE REDSHIFT EVOLUTION OF THE Ly alpha ESCAPE FRACTION AND THE DUST CONTENT OF GALAXIES2011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 730, no 1, p. 8-Article in journal (Refereed)
    Abstract [en]

    The Ly alpha emission line has been proven to be a powerful tool for studying evolving galaxies at the highest redshift. However, in order to use Ly alpha as a physical probe of galaxies, it becomes vital to know the Ly alpha escape fraction (f(esc)(Ly alpha)). Unfortunately, due to the resonant nature of Ly alpha, f(esc)(Ly alpha) may vary unpredictably and requires empirical measurement. Here, we compile Ly alpha luminosity functions (LFs) between redshifts z = 0 and 8 and, combined with Ha and ultraviolet data, assess how f(esc)(Ly alpha) evolves with redshift. We find a strong upward evolution in f(esc)(Ly alpha) over the range z = 0.3-6, which is well fit by the power law f(esc)(Ly alpha) proportional to (1 + z)(xi) with xi = (2.57(-0.12)(+0.19)). This predicts that f(esc)(Ly alpha) should reach unity at z = 11.1. By comparing f(esc)(Ly alpha) and E(B-V) in individual galaxies we derive an empirical relationship between f(esc)(Ly alpha) and E(B-V), which includes resonance scattering and can explain the redshift evolution of f(esc)(Ly alpha) between z = 0 and 6 purely as a function of the evolution in the dust content of galaxies. Beyond z approximate to 6.5, f(esc)(Ly alpha) drops more substantially, an effect attributed to either ionizing photon leakage, or an increase in the neutral gas fraction of the intergalactic medium. While distinguishing between these two scenarios may be extremely challenging, by framing the problem this way we remove the uncertainty of the halo mass from Ly alpha-based tests of reionization. We finally derive a new method by which to estimate the dust content of galaxies, based purely upon the observed Ly alpha and UV LFs. These data are characterized by an exponential with an e-folding scale of z(EBV) approximate to 3.4.

  • 44.
    Hayes, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    On the narrowband detection properties of high-redshift Lyman-alpha emitters2006In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 460, no 3, p. 681-694Article in journal (Refereed)
    Abstract [en]

    Context: Numerous surveys are currently underway or planned that aim to exploit the strengths of the Lyman-alpha emission line for cosmological purposes. Today, narrowband imaging surveys are frequently used as a probe of the distant universe.

    Aims: To investigate the reliability of the results of such high-z Lyα studies, and the validity of the conclusions that are based upon them. To determine whether reliable Lyα fluxes (FLyα) and equivalent widths (WLyα) can be estimated from narrowband imaging surveys and whether any observational biases may be present.

    Methods: We have developed software to simulate the observed line and continuum properties of synthetic Lyα galaxies in the distant universe by adopting various typical observational survey techniques. This was used to investigate how detected FLyα and WLyα vary with properties of the host galaxy or intergalactic medium: internal dust reddening; intervening Lyα absorption systems; the presence of underlying stellar populations.

    Results: None of the techniques studied are greatly susceptible to underlying stellar populations or the relative contribution of nebular gas. We find that techniques that use one off-line filter on the red side of Lyα result in highly inaccurate measurements of WLyα under all tests. Adopting two off-line filters to estimate continuum at Lyα is an improvement but is still unreliable when dust extinction is considered. Techniques that employ single narrow- and broad-band filters with the same central wavelength are not susceptible to internal dust, but Lyα absorption in the IGM can cause WLyα to be overestimated by factors of up to 2: at z=6, the median WLyα is overestimated by ~25%. The most robust approach is a SED fitting technique that fits EB-V and burst-age from synthetic models - broadband observations are needed that sample the UV continuum slope, 2175 Å dust feature, and the 4000 Å discontinuity. We also notice a redshift-dependent incompleteness that results from DLA systems close to the target LAEs, amounting to ˜ 10% at z=6.

  • 45.
    Hayes, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Atek, Hakim
    Kunth, Daniel
    Mas-Hesse, J. Miguel
    Leitherer, Claus
    Jiménez-Bailón, Elena
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy.
    The escape of Lyman photons from a young starburst: The case of Haro 112007In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 382, no 4, p. 1465-1480Article in journal (Refereed)
    Abstract [en]

    Lyman α (Lyα) is one of the dominant tools used to probe the star-forming galaxy population at high redshift (z). However, astrophysical interpretations of data drawn from Lyα alone hinge on the Lyα escape fraction which, due to the complex radiative transport, may vary greatly. Here, we map the Lyα emission from the local luminous blue compact galaxy Haro 11, a known emitter of Lyα and the only known candidate for low-z Lyman continuum emission. To aid in the interpretation, we perform a detailed ultraviolet and optical multiwavelength analysis and model the stellar population, dust distribution, ionizing photon budget, and star-cluster population. We use archival X-ray observations to further constrain properties of the starburst and estimate the neutral hydrogen column density.

    The Lyα morphology is found to be largely symmetric around a single young star-forming knot and is strongly decoupled from other wavelengths. From general surface photometry, only very slight correlation is found between Lyα and Hα, E(BV), and the age of the stellar population. Only around the central Lyα bright cluster do we find the Lyα/Hα ratio at values predicted by the recombination theory. The total Lyα escape fraction is found to be just 3 per cent. We compute that ∼90 per cent of the Lyα photons that escape do so after undergoing multiple resonance scattering events, masking their point of origin. This leads to a largely symmetric distribution and, by increasing the distance that photons must travel to escape, decreases the escape probability significantly. While dust must ultimately be responsible for the destruction of Lyα, it plays a little role in governing the observed morphology, which is regulated more by interstellar medium kinematics and geometry. We find tentative evidence for local Lyα equivalent width in the immediate vicinity of star clusters being a function of cluster age, consistent with hydrodynamic studies. We estimate the intrinsic production of ionizing photons and put further constraints of ∼9 per cent on the escaping fraction of photons at 900 Å.

  • 46.
    Hayes, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Universite de Toulouse, France.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Duval, Florent
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Adamo, Angela
    Schaerer, Daniel
    Verhamme, Anne
    Orlitova, Ivana
    Miguel Mas-Hesse, J.
    Cannon, John M.
    Atek, Hakim
    Kunth, Daniel
    Laursen, Peter
    Oti-Floranes, Hector
    Pardy, Stephen
    Rivera-Thorsen, Thöger
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Herenz, E. Christian
    THE LYMAN ALPHA REFERENCE SAMPLE. II. HUBBLE SPACE TELESCOPE IMAGING RESULTS, INTEGRATED PROPERTIES, AND TRENDS2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 782, no 1, article id 6Article in journal (Refereed)
    Abstract [en]

    We report new results regarding the Ly alpha output of galaxies, derived from the Lyman Alpha Reference Sample, and focused on Hubble Space Telescope imaging. For 14 galaxies we present intensity images in Ly alpha, H alpha, and UV, and maps of H alpha/H beta, Ly alpha equivalent width (EW), and Ly alpha/H alpha. We present Ly alpha and UV radial light profiles and show they are well-fitted by Sersic profiles, but Ly alpha profiles show indices systematically lower than those of the UV (n approximate to 1-2 instead of greater than or similar to 4). This reveals a general lack of the central concentration in Ly alpha that is ubiquitous in the UV. Photometric growth curves increase more slowly for Ly alpha than the far ultraviolet, showing that small apertures may underestimate the EW. For most galaxies, however, flux and EW curves flatten by radii approximate to 10 kpc, suggesting that if placed at high-z only a few of our galaxies would suffer from large flux losses. We compute global properties of the sample in large apertures, and show total Ly alpha luminosities to be independent of all other quantities. Normalized Ly alpha throughput, however, shows significant correlations: escape is found to be higher in galaxies of lower star formation rate, dust content, mass, and nebular quantities that suggest harder ionizing continuum and lower metallicity. Six galaxies would be selected as high-z Ly alpha emitters, based upon their luminosity and EW. We discuss the results in the context of high-z Ly alpha and UV samples. A few galaxies have EWs above 50 angstrom, and one shows f(esc)(Ly alpha) of 80%; such objects have not previously been reported at low-z.

  • 47. Hayes, Matthew
    et al.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mas-Hesse, J. Miguel
    Kunth, Daniel
    Continuum subtracting Lyman-alpha images: Low redshift studies using the Solar Blind Channel of HST/ACS2009In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 138, no 3, p. 911-922Article in journal (Refereed)
    Abstract [en]

    We are undertaking an imaging study of local star-forming galaxies in the Lyman-alpha (Lyα) emission line using the Solar Blind Channel (SBC) of the Advanced Camera for Surveys onboard the Hubble Space Telescope. Observations have been obtained in Lyα and H-alpha (Hα) and six line-free continuum filters between ~1500 Å and the I band. In a previous article, we demonstrated that the production of Lyα line-only images (i.e., continuum subtraction) in the SBC-only data set is nontrivial and that supporting data is a requirement. We here develop various methods of continuum subtraction and assess their relative performance using a variety of spectral energy distributions (SEDs) as input. We conclude that simple assumptions about the behavior of the ultraviolet continuum consistently lead to results that are wildly erroneous, and determine that a spectral fitting approach is essential. Moreover, fitting of a single component stellar or stellar+nebular spectrum is not always sufficient for realistic template SEDs and, in order to successfully recover the input observables, care must be taken to control the contribution of nebular gas and any underlying stellar population. Independent measurements of the metallicity must first be obtained, while details of the initial mass function play only a small role. We identify the need to bin together pixels in our data to obtain signal-to-noise ratios (S/Ns) of around 10 in each band before processing. At S/N = 10, we are able to recover Lyα fluxes accurate to within around 30% for Lyα lines with intrinsic equivalent width (W Lyα) of 10 Å. This accuracy improves to 10% for W Lyα = 100 Å. We describe the method of image processing applied to the observations presented in Östlin et al. and the associated data release. We also present simulations for an observing strategy for an alternative low-redshift Lyα imaging campaign using ACS/SBC using adjacent combinations of long-pass filters to target slightly higher redshift.

  • 48. Hayes, Matthew
    et al.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schaerer, Daniel
    Miguel Mas-Hesse, J.
    Leitherer, Claus
    Atek, Hakim
    Kunth, Daniel
    Verhamme, Anne
    de Barros, Stephane
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Escape of about five per cent of Lyman-alpha photons from high-redshift star-forming galaxies2010In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 464, no 7288, p. 562-565Article in journal (Refereed)
    Abstract [en]

    The Lyman-alpha (Ly alpha) emission line is the primary observational signature of star-forming galaxies at the highest redshifts(1), and has enabled the compilation of large samples of galaxies with which to study cosmic evolution(2-5). The resonant nature of the line, however, means that Ly alpha photons scatter in the neutral interstellar medium of their host galaxies, and their sensitivity to absorption by interstellar dust may therefore be greatly enhanced. This implies that the Ly alpha luminosity may be significantly reduced, or even completely suppressed. Hitherto, no unbiased empirical test of the escaping fraction (f(esc)) of Ly alpha photons has been performed at high redshifts. Here we report that the average f(esc) from star-forming galaxies at redshift z=2.2 is just 5 per cent by performing a blind narrowband survey in Ly alpha and H alpha. This implies that numerous conclusions based on Ly alpha-selected samples will require upwards revision by an order of magnitude and we provide a benchmark for this revision. We demonstrate that almost 90 per cent of star-forming galaxies emit insufficient Ly alpha to be detected by standard selection criteria(2-5). Both samples show an anti-correlation of f(esc) with dust content, and we show that Ly alpha- and H alpha-selection recovers populations that differ substantially in dust content and f(esc).

  • 49. Hayes, Matthew
    et al.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schaerer, Daniel
    Verhamme, Anne
    Mas-Hesse, J. Miguel
    Adamo, Angela
    Atek, Hakim
    Cannon, John M.
    Duval, Florent
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Herenz, E. Christian
    Kunth, Daniel
    Laursen, Peter
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Orlitova, Ivana
    Oti-Floranes, Hector
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    THE LYMAN ALPHA REFERENCE SAMPLE: EXTENDED LYMAN ALPHA HALOS PRODUCED AT LOW DUST CONTENT2013In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 765, no 2, p. L27-Article in journal (Refereed)
    Abstract [en]

    We report on new imaging observations of the Lyman alpha emission line (Ly alpha), performed with the Hubble Space Telescope, that comprise the backbone of the Lyman alpha Reference Sample. We present images of 14 starburst galaxies at redshifts 0.028 < z < 0.18 in continuum-subtracted Ly alpha, H alpha, and the far ultraviolet continuum. We show that Ly alpha is emitted on scales that systematically exceed those of the massive stellar population and recombination nebulae: as measured by the Petrosian 20% radius, RP20, Ly alpha radii are larger than those of H alpha by factors ranging from 1 to 3.6, with an average of 2.4. The average ratio of Ly alpha-to-FUV radii is 2.9. This suggests that much of the Ly alpha light is pushed to large radii by resonance scattering. Defining the Relative Petrosian Extension of Ly alpha compared to H alpha, xi(Ly alpha) = R-P20(Ly alpha)/R-P20(H alpha), we find xi(Ly alpha) to be uncorrelated with total Ly alpha luminosity. However, xi(Ly alpha) is strongly correlated with quantities that scale with dust content, in the sense that a low dust abundance is a necessary requirement (although not the only one) in order to spread Ly alpha photons throughout the interstellar medium and drive a large extended Ly alpha halo.

  • 50. Herenz, Edmund Christian
    et al.
    Gruyters, Pieter
    Orlitova, Ivana
    Hayes, Matthew
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cannon, John M.
    Roth, Martin M.
    Bik, Arjan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pardy, Stephen
    Oti-Floranes, Hector
    Miguel Mas-Hesse, J.
    Adamo, Angela
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Atek, Hakim
    Duval, Florent
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). The University of Tokyo, Japan.
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). NAF– Osservatorio Astronomico di Roma, Italy.
    Kunth, Daniel
    Laursen, Peter
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Puschnig, Johannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rivera-Thorsen, Thöger E.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schaerer, Daniel
    Verhamme, Anne
    The Lyman alpha reference sample VII. Spatially resolved H alpha kinematics2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A78Article in journal (Refereed)
    Abstract [en]

    We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z similar to 0.1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer alpha (H alpha) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly alpha radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope H alpha and Lyman alpha (Ly alpha) images. We can conjecture a causal connection between spatially resolved H alpha kinematics and Ly alpha photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion sigma(0), the shearing velocity v(shear), and the v(shear)/sigma(0) ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54 km s(-1) median) and low shearing velocities (65 km s(-1) median). The v(shear/sigma 0) values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with v(shear)/sigma(0) < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Ly alpha properties, we find that dispersion-dominated systems show higher Ly alpha equivalent widths and higher Ly alpha escape fractions than systems with v(shear)/sigma(0) > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly alpha radiation.

123 1 - 50 of 125
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf