Abstract
The reionization of hydrogen in the intergalactic medium (IGM) is a crucial landmark in the history of the Universe, but the processes through which it occurs remain mysterious. In particular, recent numerical and analytic work suggest that reionization by stellar sources is driven by large-scale density fluctuations and must be inhomogeneous on scales of many comoving Mpc. We examine the prospects for constraining the topology of neutral and ionized gas through Lya absorption of high-redshift sources. One method is to search for gaps in the Gunn-Peterson absorption troughs of luminous sources. These could occur if the line of sight passes sufficiently close to the centre of a large HII region. In contrast to previous work, we find a non-negligible (though still small) probability of observing such a gap before reionization is complete. In our model the transmission spike at z = 6.08 in the spectrum of SDSS J1148+5251 does not necessarily require overlap to have been completed at an earlier epoch. We also examine the IGM damping wing absorption of the Lya emission lines of star-forming galaxies. Because most galaxies sit inside of large H II regions, we find that the severity of absorption is significantly smaller than previously thought and decoupled from the properties of the observed galaxy. While this limits our ability to constrain the mean neutral fraction of the IGM from observations of individual galaxies, it presents the exciting possibility of measuring the size distribution and evolution of the ionized bubbles by examining the distribution of damping wing optical depths in a large sample of galaxies.
Highlights
The reionization of the intergalactic medium (IGM) constitutes a milestone in the history of the universe, because it marks the epoch at which feedback from the first generations of luminous objects transformed the universe on the largest scales
We show the cumulative probabilities that galaxies of mass mh = 109 M⊙ and mh = 1011 M⊙ are in bubbles with radius above some value in Figure 2 for the choice ζ = 40. (This choice leads to reionization at z ∼ 11.) Each curve begins at the minimum bubble size to contain such an ionizing galaxy, ζmh
We have considered two methods to study the topology of reionization through near-infrared observations of high-redshift sources
Summary
The reionization of the intergalactic medium (IGM) constitutes a milestone in the history of the universe, because it marks the epoch at which (radiative) feedback from the first generations of luminous objects transformed the universe on the largest scales. We will argue that the large HII regions cannot be neglected when interpreting Lyα absorption and make it difficult to infer the mean neutral fraction from observations of a small number of galaxies These lines do present the intriguing possibility of allowing us to measure the size distribution of HII regions throughout reionization and to constrain the inhomogeneity of the process.. These lines do present the intriguing possibility of allowing us to measure the size distribution of HII regions throughout reionization and to constrain the inhomogeneity of the process.2 Another technique is to study the absorption spectra of luminous quasars. Barkana (2002) showed explicitly that, if each galaxy is considered in isolation, transmission gaps in the Gunn-Peterson trough should be extremely rare until reionization is complete These studies did not include the biasing of sources and the correspondingly large HII regions.
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