4.7 Article

The Breakdown Scale of H I Bias Linearity

Journal

ASTROPHYSICAL JOURNAL
Volume 907, Issue 1, Pages -

Publisher

IOP Publishing Ltd
DOI: 10.3847/1538-4357/abcb8a

Keywords

H I line emission; Line intensities; Galaxy dark matter halos; Large-scale structure of the universe

Funding

  1. National Key R&D Program of China [2018YFA0404502, 2018YFA0404503, 2017YFB0203302]
  2. National Natural Science Foundation of China (NSFC) [11673014, 11761141012, 11821303, 11543006, 11833005, 11828302, 11922305, 11733004, 11773049, 11761131004, 11673015, 11421303, 11721303, U1531123]
  3. Chinese National Thousand Youth Talents Program
  4. Youth innovation Promotion Association CAS
  5. Shanghai Committee of Science and Technology [19ZR1466700]
  6. NSF [AST-1517528]

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The study investigates the nonlinear effects of halo clustering and H i content modulation on the bias of H i gas, finding that their competition results in a model-dependent redshift sweet spot near z = 1 where the bias is scale-independent down to small scales. Additionally, it is observed that the linear H i bias scales approximately linearly with redshift for z <= 3.
The 21 cm intensity mapping experiments promise to obtain the large-scale distribution of H i gas at the post-reionization epoch. In order to reveal the underlying matter density fluctuations from the H i mapping, it is important to understand how H i gas traces the matter density distribution. Both nonlinear halo clustering and nonlinear effects modulating H i gas in halos may determine the scale below which the H i bias deviates from linearity. We employ three approaches to generate the mock H i density from a large-scale N-body simulation at low redshifts, and demonstrate that the assumption of H i linearity is valid at the scale corresponding to the first peak of baryon acoustic oscillations, but breaks down at k greater than or similar to 0.1 h Mpc(-1). The nonlinear effects of halo clustering and H i content modulation counteract each other at small scales, and their competition results in a model-dependent sweet-spot redshift near z = 1, where the H i bias is scale-independent down to small scales. We also find that the linear H i bias scales approximately linearly with redshift for z <= 3.

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