The environmental dependence of H I in galaxies in the EAGLE simulations

We use the EAGLE suite of cosmological hydrodynamical simulations to study how the H I content of present-day galaxies depends on their environment. We show that EAGLE reproduces observed H I mass-environment trends very well, while semi-analytic models typically overpredict the average H I masses in dense environments. The environmental processes act primarily as an on/off switch for the H I content of satellites with M_* > 10⁹ M_⊙. At a fixed M_*, the fraction of H I-depleted satellites increase with increasing host halo mass M₂₀₀ in response to stronger environmental effects, while at a fixed M₂₀₀ it decreases with increasing satellite M_* as the gas is confined by deeper gravitational potentials. H I-depleted satellites reside mostly, but not exclusively, within the virial radius r₂₀₀ of their host halo. We investigate the origin of these trends by focusing on three environmental mechanisms: ram pressure stripping by the intragroup medium, tidal stripping by the host halo and satellite-satellite encounters. By tracking back in time the evolution of the H I-depleted satellites, we find that the most common cause of H I removal is satellite encounters. The time-scale for H I removal is typically less than 0.5 Gyr. Tidal stripping occurs in haloes of M₂₀₀ < 10¹⁴ M_⊙ within 0.5 × r₂₀₀, while the other processes act also in more massive haloes, generally within r₂₀₀. Conversely, we find that ram pressure stripping is the most common mechanism that disturbs the H I morphology of galaxies at redshift z = 0. This implies that H I removal due to satellite-satellite interactions occurs on shorter time-scales than the other processes.