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  • 1.
    Karlsson, Roland
    Stockholm University, Faculty of Science, Department of Astronomy.
    18-cm VLA observations of OH towards the Galactic Centre2003Licentiate thesis, comprehensive summary (Other academic)
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  • 2.
    Karlsson, Roland
    Stockholm University, Faculty of Science, Department of Astronomy.
    Studies of molecular clouds at the Galactic centre2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Interstellar molecular clouds play an essential role in the Universe. Such clouds are invoked for the production and destruction of stars, galaxies and gas and also for energy transport in galaxies. The Galaxy, or the Milky Way, is a large spiral galaxy, with a central bar structure, that harbours a few hundred billion stars and large amounts of gas and dust. At the centre of the Galaxy, a 4 million solar mass supermassive black hole resides, surrounded by a dense core of millions of stars, as well as molecular and dust clouds. The Galactic centre (GC) is hidden by gas and dust, such that only astronomical observations of radio-, infrared-, X-rays and gamma-rays are available for a gathering of information at the centre. In this work, I have studied neutral molecular clouds in absorption at the innermost 50 light years from the centre with the Karl Jansky Very Large Array Observatory in New Mexico in the USA, and with data from observations with the Swedish-ESO Submillimetre Telescope in Chile, and also from the orbital observatory Odin. I have detected a new stream-like feature of gas that seems to link a previously known ring of gas clouds (the CND) and the GC. Moreover, the hypothesis of feeding the CND from an outside cloud is supported by this work. Contemporary discussions in the literature that the central bar structure would act as a pump of material inwards from the spiral arms towards the GC via molecular clouds are also suggested by the data. A number of maser sources have been observed and some of those are shown to reside at shock fronts or anticipated regions of collisions between molecular clouds or at star forming regions. Unusually high water abundance was detected at the south-west part of the CND, indicative of shocks and strong turbulence. Moreover, I have produced high-resolution spectral line maps of hydroxyl (OH) absorption intensity in the four main transition lines of OH at 1612, 1720, 1665 and 1667 MHz, as well as apparent opacity and position-velocity maps of the GC region.

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  • 3.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    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).
    Martin, Sergio
    The OH-streamer in Sagittarius A revisited: Analysis of hydroxyl absorption within 10 pc from the Galactic centre2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, article id A118Article in journal (Refereed)
    Abstract [en]

    Aims. We study the structure and kinematics of the OH-streamer and the +80 km s(-1) cloud and their interactions with the circumnu-clear disk (CND) and with other molecular clouds in the vicinity of the Galactic centre (GC), and we map OH absorption at about 6 '' resolution at R <= 10 pc from the GC, with about 9 km s(-1) of velocity resolution. Methods. The VLA was used to map OH line absorption at the 1665 and 1667 MHz lambda doublet main lines of the (2)Pi(3/2) state towards the Sagittarius A complex. Results. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80 km s(-1) molecular clouds, the molecular belt, the CND, the expanding molecular ring (EMR), and the high negative velocity gas (HNVG). The OH-streamer was found to comprise three parts, head, mid, and tail, and to interact with the SS/+20, +80 km s(-1) clouds and the CND. Optical depths and column densities divided by excitation temperatures have been calculated for the OH-streamer and the +80 km s(-1) cloud. Conclusions. The OH-streamer, the SS, the +20 and +80 km s(-1) clouds, and the CND are intimately related in position and velocity space. The OH-streamer was found to be a clumpy object stretching in projection from the inner radius of the CND at about 1.8 pc from Sgr A*towards and partly engulfing Sgr A*. As a side result of our data, a possible link between the near side of the EMR and the CND's southwest lobe was found. Additionally, we found OH absorption against all four of the previously known compact H II regions A-D, located east of Sgr A East, indicating their close association with the +50 km s(-1) cloud.

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  • 4.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy.
    Martin, Sergio
    VizieR Online Data Catalog: OH-streamer in SgrA at 1665 and 1667MHz (Karlsson+, 2015)2015Other (Other academic)
    Abstract [en]

    The VLA was used to map OH line absorption at the 1665 and 1667MHz lambda doublet main lines of the 2{Pi}3/2 state towards the Sagittarius A complex. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80km/s molecular clouds, the molecular belt, the CND, the expanding molecular ring (EMR), and the high negative velocity gas (HNVG).

    Data cubes of VLA observations of the Sgr A complex at 1667- and 1665MHz OH-absorption at 7"x5" angular and 8.8km/s velocity resolution in 63 spectral channels centered at -38km/s (LSR). OH-absorption is defined as "continuum flux minus line flux". The continuum is taken as the average of 1665 and 1667 MHz maps of line free channels. Observations with the VLA in BnA and DnC arrays have been concatenated with AIPS, and data were calibrated and CLEANed with NRAO AIPS standard procedures.

    (2 data files).

  • 5.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hjalmarson, A.
    Winnberg, A.
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Olberg, M.
    Hydroxyl, water, ammonia, carbon monoxide, and neutral carbon towards the Sagittarius A complex VLA, Odin, and SEST observations2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 554, article id A141Article in journal (Refereed)
    Abstract [en]

    Aims. The Sagittarius A complex in the Galactic centre comprises an ensemble of molecular clouds of different species with a variety of geometrical and kinematic properties. This work aims to study molecular abundances, morphology, and kinematics by comparing hydroxyl, water, carbon monoxide, ammonia, and atomic carbon and some of their isotopologues, in the +50 km s(-1) cloud, the circumnuclear disk (CND), the +20 km s(-1) cloud, the expanding molecular ring and the line-of-sight spiral arm features, including the Local/Sgr arm, the -30 km s(-1) arm, and the 3-kpc arm. Methods. We observed the +50 km s(-1) cloud, the CND and the +20 km s(-1) cloud, and other selected positions at the Galactic centre with the VLA, and the Odin satellite. The VLA was used to map the 1665 and 1667 MHz OH lambda doublet main lines of the (H-2(3/2)) state, and the Odin satellite was used to map the 557 GHz H2O (1(10)-1(01)) line as well as to observe the 548 GHz (H2O)-O-18 (1(10)-1(01)) line, the 572 GHz NH3 (1(0)-0(0)) line, the 576 GHz CO J = 5-4 line and the 492 GHz C-I (P-3(1)-P-3(0)) line. Furthermore, the SEST was used to map a 4'.5 x 6' region of the SgrAcomplex in the 220 GHz (CO)-O-18 J = 2-1 line. Results. Strong OH absorption, H2O emission and absorption lines were seen at all observed positions, and the (H2O)-O-18 line was detected in absorption towards the +50 km s(-1) cloud, the CND, the +20 km s(-1)cloud, the expanding molecular ring, and the 3-kpc arm. Strong CO J = 5-4, (CO)-O-18 J = 2-1, and neutral carbon C-I emissions were seen towards the +50 and +20 km s(-1) clouds. NH3 was only detected in weak absorption originating in the line-of-sight spiral arm features. The abundances of OH and H2O in the +50 and +20 km s(-1) clouds reflect the different physical environments in the clouds, where shocks and star formation prevail in the +50 km s(-1) cloud and giving rise to a higher rate of H2O production there than in the +20 km s(-1) cloud. In the CND, cloud collisions and shocks are frequent, and the CND is also subject to intense UV-radiation emanating from the supermassive black hole and the central star cluster. The CND is rich in (HO)-O-2 and OH, and these abundances are considerably higher than in the +50 and +20 km s(-1) clouds. We compare our estimated abundances of OH, H2O, and NH3 with similar and differing results for some other sources available in the literature. As compared to the quiescent cloud values of a few x 10(-9), or lower, the H2O abundance is markedly enhanced in the front sides of the Sgr A molecular cloud cores, (2-7) x 10(-8), as observed in absorption, and highest in the CND. A similar abundance enhancement is seen in OH. The likely explanation is PDR chemistry including grain surface reactions, and perhaps also the influence of shocks. In the redward high-velocity line wings of the +50 and +20 km s(-1) clouds and the CND, the H2O abundances are estimated to be (1-6) x 10(-6) or higher, i.e., similar to the water abundances in outflows of the Orion KL and DR21 molecular clouds, which are said to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry.

  • 6.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hjalmarson, Åke
    Winnberg, Anders
    Fathi, Kambiz
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, Urban
    Olberg, Mikael
    Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex2014In: Proceedings of the International Astronomical Union, ISSN 1743-9213, E-ISSN 1743-9221, Vol. 9, no 303, p. 97-99Article in journal (Refereed)
    Abstract [en]

    We observed Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the +50 km s−1 cloud (M−0.02−0.07), the circumnuclear disk (CND) and the +20 km s−1 (M−0.13−0.08) cloud in the Sgr A complex with the VLA, Odin and SEST. Strong OH absorption, H2O emission and absorption lines were seen at all three positions. Strong C18O emissions were seen towards the +50 and +20 km s−1 clouds. The CND is rich in H2O and OH, and these abundances are considerably higher than in the surrounding clouds, indicating that shocks, star formation and clump collisions prevail in those objects. A comparison with the literature reveals that it is likely that PDR chemistry including grain surface reactions, and perhaps also the influences of shocks has led to the observed abundances of the observed molecular species studied here. In the redward high-velocity line wings of both the +50 and +20 km s−1 clouds and the CND, the very high H2O abundances are suggested to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry. Only three of the molecules are briefly discussed here. For OH and H2O three of the nine observed positions are shown, while a map of the C18O emission is provided. An extensive paper was recently published with Open Access (Karlsson et al. 2013, A&A 554, A141).

  • 7.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sjouwerman, Lorant
    NRAO.
    Whiteoak, John
    CSIRO.
    Absorption and Emission in the Four Ground-State OH Lines Observed with the VLA Towards the Galactic CentreAbsorption and Emission in the Four Ground-State OH Lines Observed at 18 cm with the VLA Towards the Galactic Centre2003In: Proceedings of the Galactic Center Workshop 2002Proceedings of the Galactic Center Workshop 2002: The central 300 parsecs of the Milky WayThe central 300 parsecs of the Milky Way, 2003, p. 223-227Conference paper (Other academic)
  • 8.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sjouwerman, Lorant O.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Whiteoak, John B.
    18-cm VLA observations of OH towards the Galactic Centre: Absorption and emission in the four ground-state OH lines2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 403, p. 1011-1021Article in journal (Refereed)
    Abstract [en]

    The OH distribution in the Sgr A Complex has been observed in the 1612-, 1665-, 1667- and 1720-MHz OH transitions with the Very Large Array (VLA) in BnA configuration. Maps are presented with a channel velocity resolution of about 9 km s -1 and with angular resolutions of  . Some clear results are highlighted here, such as absorption from the Circumnuclear Disk (CND) and the OH-Streamer inside the CND near Sgr , strong absorption towards most of the eastern and western parts of the Sgr A East shell, lack of absorption towards both Sgr A West and the compact H II-regions to the east of Sgr A East, and double-lobed structure of the High Negative Velocity Gas (HNVG) oriented northeast and southwest of Sgr , and finally compact, point-like maser emission in all four transitions, in particular a 1720-MHz maser at -132 km s -1 in the CND as counterpart to a 1720-MHz maser at +132 km s -1 in the CND.

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  • 9.
    Karlsson, Roland
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Whiteoak, John
    CSIRO.
    Gardner, Frank
    CSIRO.
    The 18 cm OH distribution in the Galactic Center Torus1987In: / [ed] D. C. Backer, New York: American Institute of Physics (AIP), 1987, p. 95-95Conference paper (Other academic)
    Abstract [en]

    The 18‐cm OH distribution in the Galactic Center region near Sgr A has been studied in all four of the 1612, 1665, 1667 and 1720 MHz OH lines using the VLA with 4 arcsec angular resolution and 9 km s 1 velocity resolution. Three 1667 MHz OH spectral line absorption maps, at +51, +25 and −1 km s 1, covering a 4’.3×4’.3 region around Sgr A are presented together with an 18‐cm continuum map. In addition, a complete set of velocity maps from +139 to −159 km s 1, covering a 3’×3’ region around the Galactic Center nuclear torus, is presented. Absorption by the +50 and +20 km s 1 molecular cloud belt is seen towards Sgr A East, but not towards Sgr A West. Absorption is also seen towards Sgr A* in the velocity ranges of +43 to −36 km s 1 and −142 to −151 km s 1. The Northeast and Southwest torus components can be traced out to velocities of +139 and −151 km s 1. A ‘‘Northwest’’ feature, starting northwest of the Western continuum arc, appears faintly at a velocity of +51 km s 1 and then migrates slightly southward until it merges with another feature at a velocity of +78 km s 1. This other feature ‘‘Sweeps’’ in towards Sgr A* as the velocity decreases from +78 to +16 km s 1.

  • 10.
    Piñol-Ferrer, Nuria
    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).
    Carignan, Claude
    Font, Joan
    Hernandez, Olivier
    Karlsson, Roland
    Stockholm University, Faculty of Science, Department of Astronomy.
    van de Ven, Glenn
    Bar pattern speed and position of the circumnuclear ringin NGC 10972014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 2, p. 971-982Article in journal (Refereed)
    Abstract [en]

    We present the first galactic-scale model of the gas dynamics of the prototype barred Seyfert 1 galaxy NGC 1097. We use large scale FaNTOmM Fabry-Perot interfer-ometric data covering the entire galactic disc and combined the distribution andkinematics maps with high resolution two-dimensional spectroscopy from the Gemini telescope. We build a dynamical model for the gravitational potential by applying the analytic solution to the equations of motion, with in the epicyclic approximation. Our model reproduces all the significant kinematic and structural signatures of thisgalaxy. We find that the primary bar is 7.9±0.6 kpc long and has a pattern speedof 36 ± 2 km s−1 kpc−1. This places the corotation radius at 8.6±0.5 kpc, the outer Lindblad resonance at 14.9±0.9 kpc and two inner Lindblad resonances at 60±5 pcand 2.9±0.1 kpc. These derivations lead to a ratio of the corotation radius over barlength of 1.0–1.2, which is in concordance with simulations of barred galaxies. Our model presents evidence that the circumnuclear ring in this galaxy is not located near any of the resonance radii in this galaxy. The ring might have once formed at the outer inner Lindblad resonance radius, and it has been migrating inward, toward the centre of the galactic gravitational potential.

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  • 11.
    Sandqvist, Aage
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Karlsson, Roland
    Stockholm University, Faculty of Science, Department of Astronomy.
    SEST and VLA observations of molecular clouds in the galactic centreSEST and VLA observations of molecular clouds in the galactic centre1990In: SEST and VLA observations of molecular clouds in the galactic centreNordic-Baltic Astronomy Meeting on Astrophysical Processes and Structures in the Universe, Heidelberg: Astronomisches Rechen-Institut , 1990, p. 71-71Conference paper (Other academic)
  • 12.
    Sandqvist, Aage
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Karlsson, Roland
    Stockholm University, Faculty of Science, Department of Astronomy.
    Whiteoak, John
    CSIRO.
    OH in the environment of Sgr A1989In: The center of the GalaxyThe Center of the Galaxy: Proceedings of the 136th Symposium of the International Astronomical Union, held in Los Angeles, U.S.A: Proceedings of the 136 th Symposium of the International Astronomical UnionProceedings of the 136th Symposium of the International Astronomical Union, held in Los Angeles, U.S.A. / [ed] M. Morris, Kluwer Academic Publishers, 1989, Vol. IAU Symo 136, p. 421-422Conference paper (Other academic)
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