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  • 1. Asad, K. M. B.
    et al.
    Koopmans, L. V. E.
    Jelic, V.
    Pandey, V. N.
    Ghosh, A.
    Abdalla, F. B.
    Bernardi, G.
    Brentjens, M. A.
    de Bruyn, A. G.
    Bus, S.
    Ciardi, B.
    Chapman, E.
    Daiboo, S.
    Fernandez, E. R.
    Harker, G.
    Iliev, I. T.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Martinez-Rubi, O.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mevius, M.
    Offringa, A. R.
    Patil, A. H.
    Schaye, J.
    Thomas, R. M.
    van der Tol, S.
    Vedantham, H. K.
    Yatawatta, S.
    Zaroubi, S.
    Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 451, no 4, p. 3709-3727Article in journal (Refereed)
    Abstract [en]

    Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual Stokes <italic toggle=yes>I maps contain leakage from polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134-166 MHz, within the central 4A degrees of the field the (<italic toggle=yes>Q, <italic toggle=yes>U) -> <italic toggle=yes>I leakage power is lower than the EoR signal at <italic toggle=yes>k < 0.3 Mpc(-1). The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, both of which could be utilized in the removal of leakage. Moreover, we could define an 'EoR window' in terms of the polarization leakage in the cylindrical power spectrum above the point spread function (PSF)-induced wedge and below <italic toggle=yes>k(ayen) similar to 0.5 Mpc(-1), and the window extended up to <italic toggle=yes>k(ayen) similar to 1 Mpc(-1) at all <italic toggle=yes>k(aSyen) when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of a parts per thousand(2) 4A degrees in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02-1 Mpc(-1).

  • 2. Ciardi, B.
    et al.
    Inoue, S.
    Abdalla, F. B.
    Asad, K.
    Bernardi, G.
    Bolton, J. S.
    Brentjens, M.
    de Bruyn, A. G.
    Chapman, E.
    Daiboo, S.
    Fernandez, E. R.
    Ghosh, A.
    Graziani, L.
    Harker, G. J. A.
    Iliev, I. T.
    Jelic, V.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kazemi, S.
    Koopmans, L. V. E.
    Martinez, O.
    Maselli, A.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Offringa, A. R.
    Pandey, V. N.
    Schaye, J.
    Thomas, R.
    Vedantham, H.
    Yatawatta, S.
    Zaroubi, S.
    Simulating the 21 cm forest detectable with LOFAR and SKA in the spectra of high-z GRBs2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 453, no 1, p. 101-105Article in journal (Refereed)
    Abstract [en]

    We investigate the feasibility of detecting 21 cm absorption features in the afterglow spectra of high redshift long Gamma Ray Bursts (GRBs). This is done employing simulations of cosmic reionization, together with estimates of the GRB radio afterglow flux and the instrumental characteristics of the LOw Frequency ARray (LOFAR). We find that absorption features could be marginally (with a S/N larger than a few) detected by LOFAR at z greater than or similar to 7 if the GRB is a highly energetic event originating from Pop III stars, while the detection would be easier if the noise were reduced by one order of magnitude, i.e. similar to what is expected for the first phase of the Square Kilometre Array (SKA1-low). On the other hand, more standard GRBs are too dim to be detected even with ten times the sensitivity of SKA1-low, and only in the most optimistic case can a S/N larger than a few be reached at z greater than or similar to 9.

  • 3.
    Datta, Kanan K.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). National Centre for Radio Astrophysics, India.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Majumdar, Suman
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Iliev, Ilian T.
    Mao, Yi
    Shapiro, Paul R.
    Ahn, Kyungjin
    Light cone effect on the reionization 21-cm signal - II. Evolution, anisotropies and observational implications2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 442, no 2, p. 1491-1506Article in journal (Refereed)
    Abstract [en]

    Measurements of the H i 21-cm power spectra from the reionization epoch will be influenced by the evolution of the signal along the line-of-sight direction of any observed volume. We use numerical as well as seminumerical simulations of reionization in a cubic volume of 607 Mpc across to study this so-called light-cone effect on the H i 21-cm power spectrum. We find that the light-cone effect has the largest impact at two different stages of reionization: one when reionization is similar to 20 per cent and other when it is similar to 80 per cent completed. We find a factor of similar to 4 amplification of the power spectrum at the largest scale available in our simulations. We do not find any significant anisotropy in the 21-cm power spectrum due to the light-cone effect. We argue that for the power spectrum to become anisotropic, the light-cone effect would have to make the ionized bubbles significantly elongated or compressed along the line of sight, which would require extreme reionization scenarios. We also calculate the two-point correlation functions parallel and perpendicular to the line of sight and find them to differ. Finally, we calculate an optimum frequency bandwidth below which the light-cone effect can be neglected when extracting power spectra from observations. We find that if one is willing to accept a 10 per cent error due to the light-cone effect, the optimum frequency bandwidth for k = 0.056 Mpc(-1) is similar to 7.5 MHz. For k = 0.15 and 0.41 Mpc(-1), the optimum bandwidth is similar to 11 and similar to 16 MHz, respectively.

  • 4. Dravins, Dainis
    et al.
    LeBohec, Stephan
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Lunds universitet.
    Nunez, Paul D.
    Optical intensity interferometry with the Cherenkov Telescope Array2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 331-347Article in journal (Refereed)
    Abstract [en]

    With its unprecedented light-collecting area for night-sky observations, the Cherenkov Telescope Array (CTA) holds great potential for also optical stellar astronomy, in particular as a multi-element intensity interferometer for realizing imaging with sub-milliarcsecond angular resolution. Such an order-of-magnitude increase of the spatial resolution achieved in optical astronomy will reveal the surfaces of rotationally flattened stars with structures in their circumstellar disks and winds, or the gas flows between close binaries. Image reconstruction is feasible from the second-order coherence of light, measured as the temporal correlations of arrival times between photons recorded in different telescopes. This technique (once pioneered by Hanbury Brown and Twiss) connects telescopes only with electronic signals and is practically insensitive to atmospheric turbulence and to imperfections in telescope optics. Detector and telescope requirements are very similar to those for imaging air Cherenkov observatories, the main difference being the signal processing (calculating cross correlations between single camera pixels in pairs of telescopes). Observations of brighter stars are not limited by sky brightness, permitting efficient CTA use during also bright-Moon periods. While other concepts have been proposed to realize kilometer-scale optical interferometers of conventional amplitude (phase-) type, both in space and on the ground, their complexity places them much further into the future than CTA, which thus could become the first kilometer-scale optical imager in astronomy.

  • 5. Jelic, V.
    et al.
    de Bruyn, A. G.
    Mevius, M.
    Abdalla, F. B.
    Asad, K. M. B.
    Bernardi, G.
    Brentjens, M. A.
    Bus, S.
    Chapman, E.
    Ciardi, B.
    Daiboo, S.
    Fernandez, E. R.
    Ghosh, A.
    Harker, G.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kazemi, S.
    Koopmans, L. V. E.
    Labropoulos, P.
    Martinez-Rubi, O.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Offringa, A. R.
    Pandey, V. N.
    Patil, A. H.
    Thomas, R. M.
    Vedantham, H. K.
    Veligatla, V.
    Yatawatta, S.
    Zaroubi, S.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Beck, R.
    Bell, M. E.
    Bentum, M. J.
    Best, P.
    Bonafede, A.
    Bregman, J.
    Breitling, F.
    Broderick, J.
    Brouw, W. N.
    Brueggen, M.
    Butcher, H. R.
    Conway, J. E.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    Dettmar, R. -J
    Duscha, S.
    Eisloeffel, J.
    Engels, D.
    Faleke, H.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Griessmeier, J.
    Gunst, A. W.
    Hamaker, J. P.
    Hassall, T. E.
    Haverkorn, M.
    Heald, G.
    Hessels, J. W. T.
    Hoeft, M.
    Hoerandel, J.
    Horneffer, A.
    van der Horst, A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    van Leeuwen, J.
    Maat, P.
    Mann, G.
    McKay-Bakowski, D.
    MeKean, J. P.
    Mank, H.
    Nelles, A.
    Morden, M. J.
    Paas, H.
    Pandey-Pornmier, M.
    Pietka, G.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Roettgering, H.
    Rowlinson, A.
    Scaife, A. M. M.
    Schwarz, D.
    Serylak, M.
    Smirnov, O.
    Steinmetz, M.
    Stewart, A.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    ter Veen, S.
    Thoudam, S.
    Toribio, C.
    Vermeulen, R.
    Voeks, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wijnholds, S. J.
    Wucknitz, O.
    Zarka, P.
    Initial LOFAR observations of epoch of reionization windows II. Diffuse polarized emission in the ELAIS-N1 field2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, p. A101-Article in journal (Refereed)
    Abstract [en]

    Aims. This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications or extracting of the cosmological 21 cm signal from the LOw-Frequency ARray - Epoch of Reionization (LOFAR-EoR) data Methods. We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results. The brightness temperature of the detected Galactic emission is on average similar to 4 K in polarized intensity and covers the range from -10 to +13 rad m(-2) in Faraday depth, The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to approximate to 1.5%. There is no indication of diffuse emission in total intensity in the interferometric data. in line with results at higher frequencies Conclusions. The wide frequency range. high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of similar to 1-2 rad m(-2) in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.

  • 6. Jelić, V.
    et al.
    de Bruyn, A. G.
    Pandey, V. N.
    Mevius, M.
    Haverkorn, M.
    Brentjens, M. A.
    Koopmans, L. V. E.
    Zaroubi, S.
    Abdalla, F. B.
    Asad, K. M. B.
    Bus, S.
    Chapman, E.
    Ciardi, B.
    Fernandez, E. R.
    Ghosh, A.
    Harker, G.
    Iliev, I. T.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kazemi, S.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Offringa, A. R.
    Patil, A. H.
    Vedantham, H. K.
    Yatawatta, S.
    Linear polarization structures in LOFAR observations of the interstellar medium in the 3C 196 field2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, article id A137Article in journal (Refereed)
    Abstract [en]

    Aims: This study aims to characterize linear polarization structures in LOFAR observations of the interstellar medium (ISM) in the 3C 196 field, one of the primary fields of the LOFAR-Epoch of Reionization key science project.

    Methods: We have used the high band antennas (HBA) of LOFAR to image this region and rotation measure (RM) synthesis to unravel the distribution of polarized structures in Faraday depth.

    Results: The brightness temperature of the detected Galactic emission is 5-15 K in polarized intensity and covers the range from -3 to +8 rad m(-2) in Faraday depth. The most interesting morphological feature is a strikingly straight filament at a Faraday depth of +0.5 rad m(-2) running from north to south, right through the centre of the field and parallel to the Galactic plane. There is also an interesting system of linear depolarization canals conspicuous in an image showing the peaks of Faraday spectra. We used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. For the first time, we see some common morphology in the RM cubes made at 150 and 350 MHz. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies and previous LOFAR observations. Based on our results, we determined physical parameters of the ISM and proposed a simple model that may explain the observed distribution of the intervening magneto-ionic medium.

    Conclusions: The mean line-of-sight magnetic field component, B-parallel to, is determined to be 0.3 +/- 0.1 mu G and its spatial variation across the 3C 196 field is 0.1 mu G. The filamentary structure is probably an ionized filament in the ISM, located somewhere within the Local Bubble. This filamentary structure shows an excess in thermal electron density (n(e)B(parallel to) > 6.2 cm(-3) mu G) compared to its surroundings.

  • 7.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Simulating observational probes of reionization2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The time in the history of the Universe when the first stars and galaxies formed and ionized the gas in the intergalactic medium is known as the Epoch of Reionization. This transformative time period, which took place within the first billion years after the Big Bang, is still relatively unexplored due to the significant difficulties associated with observing so far back in time. The theme of this thesis is tying together existing (mostly indirect) and upcoming observations with simulations.

    Papers I and II deal with Lyα emitting galaxies. The Lyα emission line is very sensitive to neutral hydrogen, which was plentiful during the Epoch of Reionization. Therefore, observations of distant Lyα galaxies may be used to indirectly tell us something about when and how reionization took place. Properly interpreting the observations is, however, far from straightforward. In Paper I we develop a new method for combining large, low-resolution simulations of the intergalactic medium with small, high-resolution simulations of individual galaxies. We use this method to reproduce existing observations. In Paper II we use the same method to make predictions for future observations.

    Another observational probe of the EoR is the 21-cm emission line from neutral hydrogen. This line is the most promising probe for directly studying the neutral gas in the early Universe, and several radio telescopes are currently gathering data to observe it. The 21-cm signal is affected by a multitude of cosmological and astrophysical effects, all of which need to be understood in order to interpret the upcoming observations. One such effect is the non-random shifts in redshifts caused by the peculiar velocity of matter flowing towards higher-density regions. This effect, known as redshift space distortions, is the topic of papers III and IV, while paper V deals with another observational effect called the lightcone effect. 

  • 8.
    Jensen, Hannes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Datta, Kanan K.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Chapman, Emma
    Abdalla, Filipe B.
    Iliev, Ilian T.
    Mao, Yi
    Santos, Mario G.
    Shapiro, Paul R.
    Zaroubi, Saleem
    Bernardi, G.
    Brentjens, M. A.
    de Bruyn, A. G.
    Ciardi, B.
    Harker, G. J. A.
    Jelic, V.
    Kazemi, S.
    Koopmans, L. V. E.
    Labropoulos, P.
    Martinez, O.
    Offringa, A. R.
    Pandey, V. N.
    Schaye, J.
    Thomas, R. M.
    Veligatla, V.
    Vedantham, H.
    Yatawatta, S.
    Probing reionization with LOFAR using 21-cm redshift space distortions2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 435, no 1, p. 460-474Article in journal (Refereed)
    Abstract [en]

    One of the most promising ways to study the epoch of reionization (EoR) is through radio observations of the redshifted 21-cm line emission from neutral hydrogen. These observations are complicated by the fact that the mapping of redshifts to line-of-sight positions is distorted by the peculiar velocities of the gas. Such distortions can be a source of error if they are not properly understood, but they also encode information about cosmology and astrophysics. We study the effects of redshift space distortions on the power spectrum of 21-cm radiation from the EoR using large-scale N-body and radiative transfer simulations. We quantify the anisotropy introduced in the 21-cm power spectrum by redshift space distortions and show how it evolves as reionization progresses and how it relates to the underlying physics. We go on to study the effects of redshift space distortions on LOFAR observations, taking instrument noise and foreground subtraction into account. We find that LOFAR should be able to directly observe the power spectrum anisotropy due to redshift space distortions at spatial scales around k similar to 0.1 Mpc(-1) after greater than or similar to 1000 h of integration time. At larger scales, sample errors become a limiting factor, while at smaller scales detector noise and foregrounds make the extraction of the signal problematic. Finally, we show how the astrophysical information contained in the evolution of the anisotropy of the 21-cm power spectrum can be extracted from LOFAR observations, and how it can be used to distinguish between different reionization scenarios.

  • 9.
    Jensen, Hannes
    et al.
    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).
    Iliev, I. T.
    Laursen, P.
    Mellema, Garrelt
    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).
    Studying reionization with the next generation of Ly alpha emitter surveys2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 444, no 3, p. 2114-2127Article in journal (Refereed)
    Abstract [en]

    We study the prospects for constraining the ionized fraction of the intergalactic medium (IGM) at z > 6 with the next generation of large Ly alpha emitter surveys. We make predictions for the upcoming Subaru Hyper Suprime-Cam (HSC) Ly alpha survey and a hypothetical spectroscopic survey performed with the JamesWebb Space Telescope (JWST). Considering various scenarios where the observed evolution of the Ly alpha luminosity function of Ly alpha emitters at z > 6 is explained partly by an increasingly neutral IGM and partly by intrinsic galaxy evolution, we show how clustering measurements will be able to distinguish between these scenarios. We find that the HSC survey should be able to detect the additional clustering induced by a neutral IGM if the global IGM neutral fraction is greater than similar to 20 per cent at z = 6.5. If measurements of the Ly alpha equivalent widths (EWs) are also available, neutral fractions as small as 10 per cent may be detectable by looking for correlation between the EW and the local number density of objects. In this case, if it should turn out that the IGM is significantly neutral at z = 6.5 and the intrinsic EW distribution is relatively narrow, the observed EWs can also be used to construct a map of the locations and approximate sizes of the largest ionized regions. For the JWST survey, the results appear a bit less optimistic. Since such surveys probe a large range of redshifts, the effects of the IGM will be mixed up with any intrinsic galaxy evolution that is present, making it difficult to disentangle the effects. However, we show that a survey with the JWST will have a possibility of observing a large group of galaxies at z similar to 7, which would be a strong indication of a partially neutral IGM.

  • 10.
    Jensen, Hannes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Laursen, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Copenhagen, Denmark.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Iliev, Ilian T.
    Sommer-Larsen, Jesper
    Shapiro, Paul R.
    On the use of Ly alpha emitters as probes of reionization2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 428, no 2, p. 1366-1381Article in journal (Refereed)
    Abstract [en]

    We use numerical simulations to study the effects of the patchiness of a partly reionized intergalactic medium (IGM) on the observability of Ly alpha emitters (LAEs) at high redshifts (z greater than or similar to 6). We present a new model that divides the Ly alpha radiative transfer into a (circum) galactic and an extragalactic (IGM) part, and investigate how the choice of intrinsic line model affects the IGM transmission results. We use our model to study the impact of neutral hydrogen on statistical observables such as the Ly alpha rest-frame equivalent width (REW) distribution, the LAE luminosity function and the two-point correlation function. We find that if the observed changes in LAE luminosity functions and equivalent width distributions between z similar to 6 and 7 are to be explained by an increased IGM neutral fraction alone, we require an extremely late and rapid reionization scenario, where the Universe was similar to 40 per cent ionized at z = 7, similar to 50 per cent ionized at z = 6.5 and similar to 100 per cent ionized at z = 6. This is in conflict with other observations, suggesting that intrinsic LAE evolution at z greater than or similar to 6 cannot be completely neglected. We show how the two-point correlation function can provide more robust constraints once future observations obtain larger LAE samples, and provide predictions for the sample sizes needed to tell different reionization scenarios apart.

  • 11.
    Jensen, Hannes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Uppsala University, Sweden.
    Majumdar, Suman
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lidz, Adam
    Iliev, Ilian T.
    Dixon, Keri L.
    The wedge bias in reionization 21-cm power spectrum measurements2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, no 1, p. 66-70Article in journal (Refereed)
    Abstract [en]

    A proposed method for dealing with foreground emission in upcoming 21-cm observations from the epoch of reionization is to limit observations to an uncontaminated window in Fourier space. Foreground emission can be avoided in this way, since it is limited to a wedge-shaped region in k(parallel to), k(perpendicular to) space. However, the power spectrum is anisotropic owing to redshift-space distortions from peculiar velocities. Consequently, the 21-cm power spectrum measured in the foreground avoidance window - which samples only a limited range of angles close to the line-of-sight direction - differs from the full redshift-space spherically averaged power spectrum which requires an average over all angles. In this paper, we calculate the magnitude of this 'wedge bias' for the first time. We find that the bias amplifies the difference between the real-space and redshift-space power spectra. The bias is strongest at high redshifts, where measurements using foreground avoidance will overestimate the redshift-space power spectrum by around 100 per cent, possibly obscuring the distinctive rise and fall signature that is anticipated for the spherically averaged 21-cm power spectrum. In the later stages of reionization, the bias becomes negative, and smaller in magnitude (less than or similar to 20 per cent).

  • 12.
    Majumdar, Suman
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Datta, Kanan K.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Choudhury, T. Roy
    Bharadwaj, Somnath
    Friedrich, Martina M.
    On the use of seminumerical simulations in predicting the 21-cm signal from the epoch of reionization2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 443, no 4, p. 2843-2861Article in journal (Refereed)
    Abstract [en]

    We present a detailed comparison of three different simulations of the epoch of reionization (EoR). The radiative transfer simulation (C-2-RAY) among them is our benchmark. Radiative transfer codes can produce realistic results, but are computationally expensive. We compare it with two seminumerical techniques: one using the same haloes as C-2-RAY as its sources (Sem-Num), and one using a conditional Press-Schechter scheme (CPS+GS). These are vastly more computationally efficient than C-2-RAY, but use more simplistic physical assumptions. We evaluate these simulations in terms of their ability to reproduce the history and morphology of reionization. We find that both Sem-Num and CPS+GS can produce an ionization history and morphology that is very close to C-2-RAY, with Sem-Num performing slightly better compared to CPS+GS. We also study different redshift-space observables of the 21-cm signal from EoR: the variance, power spectrum and its various angular multipole moments. We find that both seminumerical models perform reasonably well in predicting these observables at length scales relevant for present and future experiments. However, Sem-Num performs slightly better than CPS+GS in producing the reionization history, which is necessary for interpreting the future observations. The CPS+GS scheme, however, has the advantage that it is not restricted by the mass resolution of the dark matter density field.

  • 13.
    Mellema, Garrelt
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Koopmans, Leon V. E.
    Abdalla, Filipe A.
    Bernardi, Gianni
    Ciardi, Benedetta
    Daiboo, Soobash
    de Bruyn, A. G.
    Datta, Kanan K.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Falcke, Heino
    Ferrara, Andrea
    Iliev, Ilian T.
    Iocco, Fabio
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jelic, Vibor
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Joseph, Ronniy
    Labroupoulos, Panos
    Meiksin, Avery
    Mesinger, Andrei
    Offringa, Andre R.
    Pandey, V. N.
    Pritchard, Jonathan R.
    Santos, Mario G.
    Schwarz, Dominik J.
    Semelin, Benoit
    Vedantham, Harish
    Yatawatta, Sarod
    Zaroubi, Saleem
    Reionization and the Cosmic Dawn with the Square Kilometre Array2013In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 36, no 1-2, p. 235-318Article in journal (Refereed)
    Abstract [en]

    The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.

  • 14. Patil, Ajinkya H.
    et al.
    Zaroubi, Saleem
    Chapman, Emma
    Jelic, Vibor
    Harker, Geraint
    Abdalla, Filipe B.
    Asad, Khan M. B.
    Bernardi, Gianni
    Brentjens, Michiel A.
    de Bruyn, A. G.
    Bus, Sander
    Ciardi, Benedetta
    Daiboo, Soobash
    Fernandez, Elizabeth R.
    Ghosh, Abhik
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kazemi, Sanaz
    Koopmans, Leon V. E.
    Labropoulos, Panagiotis
    Mevius, Maaijke
    Martinez, Oscar
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Offringa, Andre R.
    Pandey, Vishhambhar N.
    Schaye, Joop
    Thomas, Rajat M.
    Vedantham, Harish K.
    Veligatla, Vamsikrishna
    Wijnholds, Stefan J.
    Yatawatta, Sarod
    Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 443, no 2, p. 1113-1124Article in journal (Refereed)
    Abstract [en]

    Several experiments are underway to detect the cosmic-redshifted 21-cm signal from neutral hydrogen from the Epoch of Reionization (EoR). Due to their very low signal-to-noise ratio, these observations aim for a statistical detection of the signal by measuring its power spectrum. We investigate the extraction of the variance of the signal as a first step towards detecting and constraining the global history of the EoR. Signal variance is the integral of the signal's power spectrum, and it is expected to be measured with a high significance. We demonstrate this through results from a simulation and parameter estimation pipeline developed for the Low-Frequency Array (LOFAR)-EoR experiment. We show that LOFAR should be able to detect the EoR in 600 h of integration using the variance statistic. Additionally, the redshift (z(r)) and duration (Delta z) of reionization can be constrained assuming a parametrization. We use an EoR simulation of z(r) = 7.68 and Delta(z) = 0.43 to test the pipeline. We are able to detect the simulated signal with a significance of four standard deviations and extract the EoR parameters as z(r) = 7.72(-0.18)(+0.37) and Delta z = 0.53(-0.23)(+0.12) in 600 h, assuming that systematic errors can be adequately controlled. We further show that the significance of detection and constraints on EoR parameters can be improved by measuring the cross-variance of the signal by cross-correlating consecutive redshift bins.

  • 15. Vedantham, H. K.
    et al.
    Koopmans, L. V. E.
    de Bruyn, A. G.
    Wijnholds, S. J.
    Brentjens, M.
    Abdalla, F. B.
    Asad, K. M. B.
    Bernardi, G.
    Bus, S.
    Chapman, E.
    Ciardi, B.
    Daiboo, S.
    Fernandez, E. R.
    Ghosh, A.
    Harker, G.
    Jelic, V.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kazemi, S.
    Lambropoulos, P.
    Martinez-Rubi, O.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mevius, M.
    Offringa, A. R.
    Pandey, V. N.
    Patil, A. H.
    Thomas, R. M.
    Veligatla, V.
    Yatawatta, S.
    Zaroubi, S.
    Anderson, J.
    Asgekar, A.
    Bell, M. E.
    Bentum, M. J.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Broderick, J.
    Bruggen, M.
    Butcher, H. R.
    Corstanje, A.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    Duscha, S.
    Eisloeffel, J.
    Engels, D.
    Falcke, H.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Griessmeier, J.
    Gunst, A. W.
    Hassall, T. E.
    Heald, G.
    Hoeft, M.
    Hoerandel, J.
    Iacobelli, M.
    Juette, E.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Mulcahy, D. D.
    Munk, H.
    Nelles, A.
    Norden, M. J.
    Orru, E.
    Pandey-Pommier, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Renting, A.
    Roettgering, H.
    Schwarz, D.
    Shulevski, A.
    Smirnov, O.
    Stappers, B. W.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    ter Veen, S.
    Thoudam, S.
    Toribio, C.
    Vocks, C.
    Wise, M. W.
    Wucknitz, O.
    Zarka, P.
    Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, no 3, p. 2291-2305Article in journal (Refereed)
    Abstract [en]

    We present radio observations of the Moon between 35 and 80 MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies 35 < nu < 80 MHz since it is 'colder' than the diffuse Galactic background it occults, (ii) using the (negative) flux of the lunar disc, we can reconstruct the spectrum of the diffuse Galactic emission with the lunar thermal emission as a reference, and (iii) that reflected RFI (radio-frequency interference) is concentrated at the centre of the lunar disc due to specular nature of reflection, and can be independently measured. Our RFI measurements show that (i) Moon-based Cosmic Dawn experiments must design for an Earth-isolation of better than 80 dB to achieve an RFI temperature < 1 mK, (ii) Moon-reflected RFI contributes to a dipole temperature less than 20 mK for Earth-based Cosmic Dawn experiments, (iii) man-made satellite-reflected RFI temperature exceeds 20 mK if the aggregate scattering cross-section of visible satellites exceeds 175 m(2) at 800 km height, or 15 m(2) at 400 km height. Currently, our diffuse background spectrum is limited by sidelobe confusion on short baselines (10-15 per cent level). Further refinement of our technique may yield constraints on the redshifted global 21 cm signal from Cosmic Dawn (40 > z > 12) and the Epoch of Reionization (12 > z > 5).

  • 16.
    Zackrisson, Erik
    et al.
    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).
    Wiik, Kaj
    Jonsson, Jakob
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Scott, Pat
    Datta, Kanan K.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Friedrich, Martina M.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. 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).
    Rydberg, Claes-Erik
    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).
    Hunting for dark halo substructure using submilliarcsecond-scale observations of macrolensed radio jets2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 431, no 3, p. 2172-2183Article in journal (Refereed)
    Abstract [en]

    Dark halo substructure may reveal itself through secondary, small-scale gravitational lensing effects on light sources that are macrolensed by a foreground galaxy. Here, we explore the prospects of using Very Long Baseline Interferometry (VLBI) observations of multiply-imaged quasar jets to search for submilliarcsecond-scale image distortions produced by various forms of dark substructures in the 10(3)-10(8) M-circle dot mass range. We present lensing simulations relevant for the angular resolutions attainable with the existing European VLBI Network, the global VLBI array and an upcoming observing mode in which the Atacama Large Millimeter Array (ALMA) is connected to the global VLBI array. While observations of this type would not be sensitive to standard cold dark matter subhaloes, they can be used to detect the more compact forms of halo substructure predicted in alternative structure formation scenarios. By mapping approximately five strongly lensed systems, it should be possible to detect or robustly rule out primordial black holes in the 10(3)-10(6) M-circle dot mass range if they constitute greater than or similar to 1 per cent of the dark matter in these lenses. Ultracompact minihaloes are harder to detect using this technique, but 10(6)-10(8) M-circle dot ultracompact minihaloes could in principle be detected if they constitute greater than or similar to 10 per cent of the dark matter.

  • 17.
    Zackrisson, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Inoue, Akio K.
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    THE SPECTRAL EVOLUTION OF THE FIRST GALAXIES. II. SPECTRAL SIGNATURES OF LYMAN CONTINUUM LEAKAGE FROM GALAXIES IN THE REIONIZATION EPOCH2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 777, no 1, p. 39-Article in journal (Refereed)
    Abstract [en]

    The fraction of ionizing photons that escape (f(esc)) from z greater than or similar to 6 galaxies is an important parameter for assessing the role of these objects in the reionization of the universe, but the opacity of the intergalactic medium precludes a direct measurement of f(esc) for individual galaxies at these epochs. We argue that since f(esc) regulates the impact of nebular emission on the spectra of galaxies, it should nonetheless be possible to indirectly probe f(esc) well into the reionization epoch. As a first step, we demonstrate that by combining measurements of the rest-frame UV slope beta with the equivalent width of the H beta emission line, galaxies with very high Lyman continuum escape fractions (f(esc) >= 0.5) should be identifiable up to z approximate to 9 through spectroscopy with the upcoming James Webb Space Telescope (JWST). By targeting strongly lensed galaxies behind low-redshift galaxy clusters, JWST spectra of sufficiently good quality can be obtained for M-1500 less than or similar to -16.0 galaxies at z approximate to 7 and for M-1500 less than or similar to -17.5 galaxies at z approximate to 9. Dust-obscured star formation may complicate the analysis, but supporting observations with ALMA or the planned SPICA mission may provide useful constraints on this effect.

1 - 17 of 17
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