Catch Me if You Can: Biased Distribution of Lyα-emitting Galaxies according to the Viewing Direction

Momose, Rieko and Shimasaku, Kazuhiro and Nagamine, Kentaro and Shimizu, Ikkoh and Kashikawa, Nobunari and Ando, Makoto and Kusakabe, Haruka (2021) Catch Me if You Can: Biased Distribution of Lyα-emitting Galaxies according to the Viewing Direction. The Astrophysical Journal Letters, 912 (2). L24. ISSN 2041-8205

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Abstract

We report that Lyα-emitting galaxies (LAEs) may not faithfully trace the cosmic web of neutral hydrogen (H i), but their distribution is likely biased depending on the viewing direction. We calculate the cross-correlation function (CCF) between galaxies and Lyα forest transmission fluctuations on the near and far sides of the galaxies separately, for three galaxy samples at z ∼ 2: LAEs, [O iii] emitters (O3Es), and continuum-selected galaxies. We find that only LAEs have anisotropic CCFs, with the near side one showing lower signals up to r = 3–4 h−1 comoving Mpc. This means that the average H i density on the near side of LAEs is lower than that on the far side by a factor of 2.1 under the fluctuating Gunn–Peterson approximation. Mock LAEs created by assigning Lyα equivalent width (${{EW}}_{{\rm{Ly}}\alpha }^{{\rm{obs}}}$) values to O3Es with an empirical relation also show similar, anisotropic CCFs if we use only objects with higher ${{EW}}_{{\rm{Ly}}\alpha }^{{\rm{obs}}}$ than a certain threshold. These results indicate that galaxies on the far side of a dense region are more difficult to be detected ("hidden") in Lyα because Lyα emission toward us is absorbed by dense neutral hydrogen. If the same region is viewed from a different direction, a different set of LAEs will be selected as if galaxies are playing hide-and-seek using H i gas. Care is needed when using LAEs to search for overdensities.

Item Type: Article
Subjects: Open Research Librarians > Physics and Astronomy
Depositing User: Unnamed user with email support@open.researchlibrarians.com
Date Deposited: 11 May 2023 09:02
Last Modified: 12 Jan 2024 07:23
URI: http://stm.e4journal.com/id/eprint/917

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