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  • 1.
    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).
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mao, Yi
    Iliev, Ilian T.
    Shapiro, Paul R.
    Ahn, Kyungjin
    Light-cone effect on the reionization 21-cm power spectrum2012In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 424, no 3, p. 1877-1891Article in journal (Refereed)
    Abstract [en]

    Observations of redshifted 21-cm radiation from neutral hydrogen during the epoch of reionization are considered to constitute the most promising tool to probe that epoch. One of the major goals of the first generation of low-frequency radio telescopes is to measure the 3D 21-cm power spectrum. However, the 21-cm signal could evolve substantially along the line-of-sight (LOS) direction of an observed 3D volume, since the received signal from different planes transverses to the LOS originated from different look-back times and could therefore be statistically different. Using numerical simulations we investigate this so-called light-cone effect on the spherically averaged 3D 21-cm power spectrum. For this version of the power spectrum, we find that the effect mostly averages out and observe a smaller change in the power spectrum compared to the amount of evolution in the mean 21-cm signal and its rms variations along the LOS direction. Nevertheless, changes up to similar to 50?per cent at large scales are possible. In general, the power is enhanced/suppressed at large/small scales when the effect is included. The cross-over mode below/above which the power is enhanced/suppressed moves towards larger scales as reionization proceeds. When considering the 3D power spectrum we find it to be anisotropic at the late stages of reionization and on large scales. The effect is dominated by the evolution of the ionized fraction of hydrogen during reionization and including peculiar velocities hardly changes these conclusions. We present simple analytical models which explain qualitatively all the features we see in the simulations.

  • 2.
    Giri, Sambit K.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Aldheimer, Thomas
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dixon, Keri L.
    Iliev, Ilian T.
    Neutral island statistics during reionization from 21-cm tomographyManuscript (preprint) (Other academic)
    Abstract [en]

    We present the prospects of extracting information about the Epoch of Reionization by identifying the remaining neutral regions, referred to as islands, in tomographic observations of the redshifted 21-cm signal. Using simulated data sets we show that at late times the 21-cm power spectrum is fairly insensitive to the details of the reionization process but that the properties of the neutral islands can distinguish between different reionization scenarios. We compare the properties of these islands with those of ionized bubbles. At equivalent volume filling fractions, neutral islands tend to be fewer in number but larger compared to the ionized bubbles. In addition, the evolution of the size distribution of neutral islands is found to be slower than that of the ionized bubbles and also their percolation behaviour differs substantially. Even though the neutral islands are relatively rare, they will be easier to identify in observations with the low frequency component of the Square Kilometre Array (SKA-Low) due to their larger size and the lower noise levels at lower redshifts. The size distribution of neutral islands at the late stages of reionization is found to depend on the source properties, such as the ionizing efficiency of the sources and their minimum mass. We find the longest line of sight through a neutral region to be more than 100 comoving megaparsecs until very late stages (90-95 per cent reionized), which may have relevance for the long absorption trough at z = 5.6 − 5.8 in the spectrum of quasar ULASJ0148+0600.

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