Atomic hydrogen in IllustrisTNG galaxies: the impact of environment parallelled with local 21-cm surveys

Adam R. H. Stevens, Benedikt Diemer, Claudia del P. Lagos, Dylan Nelson, Annalisa Pillepich, Toby Brown, Barbara Catinella, Lars Hernquist, Rainer Weinberger, Mark Vogelsberger, Federico Marinacci

Published 2018-10-29Version 1

We investigate the influence of environment on the cold-gas properties of galaxies at z=0 within the TNG100 cosmological, magnetohydrodynamic simulation, part of the IllustrisTNG suite. We extend previous post-processing methods for breaking gas cells into their atomic and molecular phases, and build detailed mocks to comprehensively compare to the latest surveys of atomic hydrogen (HI) in nearby galaxies, namely ALFALFA and xGASS. We use TNG100 to explore the HI content, star formation activity, and angular momentum of satellite galaxies, each as a function of environment, and find that satellites are typically a factor of ~3 poorer in HI than centrals of the same stellar mass, with the exact offset depending sensitively on parent halo mass. Due to the significant beam size of Arecibo, contributions from diffuse halo gas and gas in other galaxies in the same line of sight crucially lead to larger HI mass measurements of galaxies in the mocks, ultimately giving rise to alignment with observations. This effect is naturally greater for satellites than centrals, especially at lower masses, as satellites are never isolated by definition. Despite this success, HI stripping in TNG100 satellites is closely accompanied by quenching, in tension with observational data that instead favour that HI is preferentially stripped before star formation is reduced.