Star formation quenching in simulated group and cluster galaxies: When, how, and why?

TL;DR

This study uses cosmological hydrodynamical simulations to analyze the timing, mechanisms, and reasons behind star formation quenching in group and cluster galaxies, highlighting the dominant role of ram pressure stripping over strangulation.

Contribution

It provides new insights into the quenching process, emphasizing the importance of ram pressure stripping and its timing relative to galaxy accretion, based on detailed simulation analysis.

Findings

Quenching occurs from 2 Gyr before to over 4 Gyr after accretion.

Ram pressure stripping is the primary mechanism removing star-forming gas.

Stripping is more effective at early times and affects the gas within galaxies and their extended haloes.

Abstract

Star formation is observed to be suppressed in group and cluster galaxies compared to the field. To gain insight into the quenching process, we have analysed ~2000 galaxies formed in the GIMIC suite of cosmological hydrodynamical simulations. The time of quenching varies from ~2 Gyr before accretion (first crossing of r200,c) to >4 Gyr after, depending on satellite and host mass. Once begun, quenching is rapid (>~ 500 Myr) in low-mass galaxies (M* < 10^10 M_Sun), but significantly more protracted for more massive satellites. The simulations predict a substantial role of outflows driven by ram pressure -- but not tidal forces -- in removing the star-forming interstellar matter (ISM) from satellite galaxies, especially dwarfs (M* ~ 10^9 M_Sun) where they account for nearly two thirds of ISM loss in both groups and clusters. Immediately before quenching is complete, this fraction rises to ~80% even for Milky Way analogues (M* ~ 10^10.5 M_Sun) in groups (M_host ~ 10^13.5 M_Sun). We show that (i) ISM stripping was significantly more effective at early times than at z = 0; (ii) approximately half the gas is stripped from `galactic fountains' and half directly from the star forming disk; (iii) galaxies undergoing stripping experience ram pressure up to ~100 times the average at a given group/cluster-centric radius, because they are preferentially located in overdense ICM regions. Remarkably, stripping causes at most half the loss of the extended gas haloes surrounding our simulated satellites. These results contrast sharply with the current picture of strangulation -- removal of the ISM through star formation after stripping of the hot halo -- being the dominant mechanism quenching group and cluster satellites.