21-cm signatures of residual H I inside cosmic H II regions during reionization (original) (raw)
Related papers
arXiv: Cosmology and Nongalactic Astrophysics, 2019
The epoch of reionization, when photons from early galaxies ionized the intergalactic medium about a billion years after the Big Bang, is the last major phase transition in the Universe's history. Measuring the characteristics of the transition is important for understanding early galaxies and the cosmic web and for modeling dwarf galaxies in the later Universe. But such measurements require probes of the intergalactic medium itself. Here we describe how the 21-cm line of neutral hydrogen provides a powerful probe of the reionization process and therefore important constraints on both the galaxies and intergalactic absorbers at that time. While existing experiments will make precise statistical measurements over the next decade, we argue that improved 21-cm analysis techniques - allowing imaging of the neutral gas itself - as well as improved theoretical models, are crucial for testing our understanding of this important era.
Monthly Notices of the Royal Astronomical Society, 2020
A number of current and future experiments aim to detect the reionization of neutral hydrogen by the first stars and galaxies in the Universe via the redshifted 21 cm line. Using the bluetides simulation, we investigate the measurement of an average ionized region towards the beginning of reionization by stacking redshifted 21 cm images around optically identified bright galaxies using mock observations. We find that with an SKA 1000 h observation, assuming perfect foreground subtraction, a 5σ detection of a stacked H ii region can be made with 30 images around some of the brightest galaxies in bluetides (brighter than MUV < −22.75) at z = 9 (corresponding to a neutral fraction of 90.1 per cent in our model). We present simulated relationships between the UV magnitude of galaxies, the sizes of the ionized regions they reside in, and the shape of the stacked profiles. These mock observations can also distinguish between scenarios where the intergalactic medium is in net emission o...
Observing the reionization epoch through 21-centimetre radiation
Monthly Notices of the Royal Astronomical Society, 2004
We study the observability of the reionization epoch through the 21-cm hyperfine transition of neutral hydrogen. We use a high-resolution cosmological simulation (including hydrodynamics) together with a fast radiative transfer algorithm to compute the evolution of 21-cm emission from the intergalactic medium (IGM) in several different models of reionization. We show that the mean brightness temperature of the IGM drops from δT b ∼ 25 mK to ∼10 −2 mK during overlap (over a frequency interval ν ∼ 25 MHz), while the root mean square fluctuations on small scales drop abruptly from δT 2 b 1/2 ∼ 10 mK to ∼10 −1 mK at the end of overlap. We show that 21-cm observations can efficiently discriminate models with a single early reionization epoch from models with two distinct reionization episodes.
Probing Reionization with the 21 cm Galaxy Cross-Power Spectrum
Astrophysical Journal, 2009
The cross-correlation between high redshift galaxies and 21 cm emission from the high redshift intergalactic medium (IGM) promises to be an excellent probe of the Epoch of Reionization (EoR). On large scales, the 21 cm and galaxy fields are anti-correlated during most of the reionization epoch. However, on scales smaller than the size of the H II regions around detectable galaxies, the two fields become roughly uncorrelated. Consequently, the 21 cm-galaxy cross power spectrum provides a tracer of bubble growth during reionization, with the signal turning over on progressively larger scales as reionization proceeds. The precise turnover scale depends on the minimum host mass of the detectable galaxies, and the galaxy selection technique. Measuring the turnover scale as a function of galaxy luminosity constrains the characteristic bubble size around galaxies of different luminosities. The cross spectrum becomes positive on small scales if ionizing photons fail to escape from low mass galaxies, and these galaxies are detectable longward of the hydrogen ionization edge, because in this case some identifiable galaxies lie outside of ionized regions. LOFAR can potentially measure the 21 cm-galaxy cross spectrum in conjunction with mild extensions to the existing Subaru survey for z=6.6z=6.6z=6.6 Lyman-alpha emitters, while the MWA is slightly less sensitive for detecting the cross spectrum. A futuristic galaxy survey covering a sizable fraction of the MWA field of view ($\sim 800$ deg$^2$) can probe the scale dependence of the cross spectrum, constraining the filling factor of H II regions at different redshifts during reionization, and providing other valuable constraints on reionization models.
Can 21-cm observations discriminate between high-mass and low-mass galaxies as reionization sources?
Monthly Notices of the Royal Astronomical Society, 2012
The prospect of detecting the first galaxies by observing their impact on the intergalactic medium (IGM) as they reionized it during the first billion years leads us to ask whether such indirect observations are capable of diagnosing which types of galaxies were most responsible for reionization. We attempt to answer this with new large-scale radiative transfer simulations of reionization including the entire mass range of atomically cooling haloes (M > 10 8 M). We divide these haloes into two groups, high-mass, atomically cooling haloes, or HMACHs (M > 10 9 M), and low-mass, atomically cooling haloes, or LMACHs (10 8 < M < 10 9 M), the latter being susceptible to negative feedback due to Jeans mass filtering in ionized regions, which leads to a process we refer to as self-regulation. We focus here on predictions of the redshifted 21-cm emission, to see if upcoming observations are capable of distinguishing a universe ionized primarily by HMACHs from one in which both HMACHs and LMACHs are responsible, and to see how these results depend upon the uncertain source efficiencies. We find that 21-cm fluctuation power spectra observed by the first-generation Epoch of Reionization 21-cm radio interferometer arrays should be able to distinguish the case of reionization by HMACHs alone from that by both HMACHs and LMACHs, together. Some reionization scenarios, e.g. one with abundant low-efficiency sources versus one with self-regulation, yield very similar power spectra and rms evolution and thus can only be discriminated by their different mean reionization history and 21-cm probability distribution function (PDF) distributions. We also find that the skewness of the 21-cm PDF distribution smoothed with Low Frequency Array (LOFAR)-like resolution shows a clear feature correlated with the rise of the rms due to patchiness. This is independent of the reionization scenario and thus provides a new approach for detecting the rise of large-scale patchiness. The peak epoch of the 21-cm rms fluctuations depends significantly on the beam and bandwidth smoothing size as well as on the reionization scenario and can occur for ionized fractions as low as 30 per cent and as high as 70 per cent. Measurements of the mean photoionization rates are sensitive to the average density of the regions being studied and therefore could be strongly skewed in certain cases. Finally, the simulation volume employed has very modest effects on the results during the early and intermediate stages of reionization, but late-time signatures could be significantly affected.
Constraining large-scale H i bias using redshifted 21-cm signal from the post-reionization epoch
Monthly Notices of the Royal Astronomical Society, 2012
In the absence of complex astrophysical processes that characterize the reionization era, the 21-cm emission from neutral hydrogen (H I) in the post-reionization epoch is believed to be an excellent tracer of the underlying dark matter distribution. Assuming a background cosmology, it is modelled through (i) a bias function b(k, z), which relates H I to the dark matter distribution and (ii) a mean neutral fraction (x H I) which sets its amplitude. In this paper, we investigate the nature of large-scale H I bias. The post-reionization H I is modelled using gravity only N-body simulations and a suitable prescription for assigning gas to the dark matter haloes. Using the simulated bias as the fiducial model for H I distribution at z ≤ 4, we have generated a hypothetical data set for the 21-cm angular power spectrum (C) using a noise model based on parameters of an extended version of the Giant Metrewave Radio Telescope (GMRT). The binned C is assumed to be measured with S/N 4 in the range 400 ≤ ≤ 8000 at a fiducial redshift z = 2.5. We explore the possibility of constraining b(k) using the principal component analysis on these simulated data. Our analysis shows that in the range 0.2 < k < 2 Mpc −1 , the simulated data set cannot distinguish between models exhibiting different k-dependences, provided 1 b(k) 2 which sets the 2σ limits. This justifies the use of linear bias model on large scales. The largely uncertainx H I is treated as a free parameter resulting in degradation of the bias reconstruction. The given simulated data are found to constrain the fiducialx H I with an accuracy of ∼4 per cent (2σ error). The method outlined here could be successfully implemented on future observational data sets to constrain b(k, z) andx H I and thereby enhance our understanding of the low-redshift Universe.
Monthly Notices of The Royal Astronomical Society, 2006
We present detailed predictions for the redshifted 21cm signal from the epoch of reionization. These predictions are obtained from radiative transfer calculations on the results of large scale (100/h Mpc), high dynamic range, cosmological simulations. We consider several scenarios for the reionization history, of both early and extended reionization. From the simulations we construct and analyze a range of observational