The local PNG bias of neutral Hydrogen, ${\rm H_I}$

Abstract

We use separate universe simulations with the IllustrisTNG galaxy formation model to predict the local PNG bias parameters b φ and b φδ of atomic neutral hydrogen, H I . These parameters and their relation to the linear density bias parameter b 1 play a key role in observational constraints of the local PNG parameter f nl using the H I power spectrum and bispectrum. Our results show that the popular calculation based on the universality of the halo mass function overpredicts the b φ (b 1 ) and b φδ (b 1 ) relations measured in the simulations. In particular, our results show that at z 1 the H I power spectrum is more sensitive to f nl compared to previously thought (b φ is more negative), but is less sensitive at other epochs (b φ is less positive). We discuss how this can be explained by the competition of physical effects such as that large-scale gravitational potentials with local PNG (i) accelerate the conversion of hydrogen to heavy elements by star formation, (ii) enhance the effects of baryonic feedback that eject the gas to regions more exposed to ionizing radiation, and (iii) promote the formation of denser structures that shield the H I more efficiently. Our numerical results can be used to revise existing forecast studies on f nl using 21cm line-intensity mapping data. Despite this first step towards predictions for the local PNG bias parameters of H I , we emphasize that more work is needed to assess their sensitivity on the assumed galaxy formation physics and H I modeling strategy.

Unveiling the Universe with emerging cosmological probes

“…The aforementioned surveys can probe ultra-large scales and constrain the primordial non-Gaussianity parameter, f NL , to a level rðf NL Þ $ 1 (Camera et al 2013;Alonso et al 2015a;Karagiannis et al 2020;Barreira 2022). However, foreground removal effects can lead to large degeneracies and biased estimates (Cunnington et al 2020a).…”

Validating galaxy clustering models with Fixed & Paired and Matched-ICs simulations: application to Primordial Non-Gaussianities

“…An additional advantage of using Fix, Pair and Match together is that one can use a high mass resolution in order to resolve well the halos of interests for future surveys (log𝑀 ℎ ∼ 11 for Euclid and DESI) in a 𝑉 ∼ 1(Gpc/ℎ) 3 box with reasonable computing resources (𝑁 = 4096 3 in UNITsim), while keeping a reduced uncertainty on 𝑓 NL (or 𝑝 or 𝑏 𝜙 ). This way, one could also use semi-analytical models of galaxy formation (as recently done in Zhai et al 2021;Knebe et al 2022, to populate 14 https://www.desi.lbl.gov/ 15 https://sci.esa.int/web/euclid UNITsim with H-𝛼 galaxies for Roman/Euclid) to understand the effect of galaxy formation on 𝑝 or 𝑏 𝜙 for different tracers (as done in Barreira et al 2020;Barreira 2021).…”

Can we actually constrain $f_{\rm NL}$ using the scale-dependent bias effect? An illustration of the impact of galaxy bias uncertainties using the BOSS DR12 galaxy power spectrum

“…[52], and for neutral Hydrogen in IllustrisTNG in Ref. [73], but more work is needed to establish the robustness and connection of these early results to the real Universe.…”

“…• Neutral hydrogen (21cm) with IllustrisTNG. Reference [73] ) relation of the BOSS DR12 galaxies (or of any other tracer of the large-scale structure) is currently not known, which is precisely the issue that we discuss in this paper. Note also that this is a problem that cannot be resolved with the multitracer technique [74,75], since each new galaxy sample that enters the multitracer analysis has its own associated b φ parameter, and the degeneracy with f nl remains unbroken [52,53].…”