H i as a probe of the large-scale structure in the post-reionization universe

Abstract

We model the distribution of neutral hydrogen (H i) in the post‐reionization universe. This model uses gravity‐only N‐body simulations and an ansatz to assign H i to dark matter haloes that is consistent with observational constraints and theoretical models. We resolve the smallest haloes that are likely to host H i in the simulations; care is also taken to ensure that any errors due to the finite size of the simulation box are small. We then compute the smoothed one‐point probability distribution function and the power spectrum of fluctuations in H i. This is compared with other predictions that have been made using different techniques. We highlight the significantly high bias for the H i distribution at small scales. This aspect has not been discussed before. We then discuss the prospects of the detection with the Murchison Widefield Array (MWA), Giant Meterwave Radio Telescope (GMRT) and the hypothetical MWA5000. The MWA5000 can detect visibility correlations at large angular scales at all redshifts in the post‐reionization era. The GMRT can detect visibility correlations at lower redshifts; specifically there is a strong case for a survey at z≃ 1.3. We also discuss prospects for direct detection of rare peaks in the H i distribution using the GMRT. We show that direct detection should be possible with an integration time that is comparable to, or even less than, the time required for a statistical detection. Specifically, it is possible to make a statistical detection of the H i distribution by measuring the visibility correlation and direct detection of rare peaks in the H i distribution at z≃ 1.3 with the GMRT in less than 1000 h of observations.

Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

“…This is clearly in tension with our results but also with the lower limits on the HI mass of the Sausage and Virgo clusters. The model 2 of Bagla et al (2010) lies in between models 1 and 3, and therefore the discrepancies among our results and the observational limits will be larger than those obtained by employing the model 3. We therefore concentrate our analysis in the model 3 of Bagla et al (2010).…”

“…As discussed in the introduction, the shape and amplitude of the function MHI(M, z) is of primary importance for future surveys that aim at putting constraints on the cosmological parameters using intensity mapping. We now compare our findings with the theoretical model of Bagla et al (2010), which has been commonly used in the literature to perform forecasts (Camera et al 2013;Bull et al 2015;Villaescusa-Navarro et al 2014, 2015bCarucci et al 2015;Villaescusa-Navarro et al 2015a) and to create mock 21cm intensity mapping maps (Seehars et al 2015). Bagla et al (2010) proposed a functional form for the MHI(M, z) function as follows…”

“…In this section we compare our results against the predictions of the Bagla et al (2010) model and study the implications for 21cm intensity mapping. As discussed in the introduction, the shape and amplitude of the function MHI(M, z) is of primary importance for future surveys that aim at putting constraints on the cosmological parameters using intensity mapping.…”

“…In their model 1, Bagla et al (2010) proposed that halos with circular velocities larger than 200 km/s (∼ 2 × 10 12 h −1 M at z = 0) do not host any HI at all. This is clearly in tension with our results but also with the lower limits on the HI mass of the Sausage and Virgo clusters.…”

“…Theoretical models like the one presented in Bagla et al (2010) propose a phenomenological function for MHI(M, z) making the hypothesis that galaxy clusters do not host a significant amount of neutral hydrogen. This hypothesis relies on the fact that observations point out that galaxies in clusters are HI deficient (Solanes et al 2001;Gavazzi et al 2005Gavazzi et al , 2006Taylor et al 2012Taylor et al , 2013Catinella et al 2013;Dénes et al 2014).…”