The trajectories of galaxies in groups: mass-loss and preprocessing

Abstract

We present a study of environmental effects and preprocessing in a large galaxy group using a high-resolution, zoom-in simulation run with the gasoline2 hydrodynamics code. We categorize galaxies that were always in distinct haloes as unaccreted, galaxies that were distinct before accretion onto the main group as single, and galaxies that were in external sub-groups before accretion onto the main group as grouped.The unaccreted galaxy population experiences steady growth in dark matter, gas and stellar mass. Both single-and group-accreted galaxies begin to lose dark matter and gas after first accretion onto any host but continue to grow in stellar mass. Individual trajectories show that galaxies cease mass growth within roughly three virial radii of the main group. Single galaxies continue to form stars until the group virial radius is crossed, when they begin to lose both dark matter and gas. Grouped galaxies peak in mass when joining their external sub-group, indicating that they experience preprocessing. Most accreted galaxies retain their accumulated stellar mass. The total mass loss is dominated by tidal stripping, with evidence for additional gas stripping via ram pressure. Most accreted galaxies are quenched ∼(0.5-2.5) Gyr after accretion onto any group.These differing histories place unaccreted, single and grouped galaxies in distinct regions of the stellar mass-to-halo mass (SMHM) relation. This suggests that preprocessed galaxies are a key source of scatter in the SMHM relation for mixed galaxy populations.

The fate of disc galaxies in IllustrisTNG clusters

“…Note that here M DM,tot is the mass of all gravitationally bound DM particles of the subhalo. Importantly, the cluster and control discs span different ranges in initial stellar-to-DM mass ratios, a further manifestation of the preprocessing of the cluster discs, which have likely lost some dark matter in their previous host haloes (see also Joshi et al 2019;Engler et al 2020); even without actual preprocessing, the galaxies have likely experienced the effects of their future hosts at large distances, which would also contribute to the reduction in initial stellar-to-DM mass ratios (e.g. see Behroozi et al 2014).…”

Strongly lensed cluster substructures are not in tension with ΛCDM

“…6 of Schaller et al 2015a), many of the cluster subhaloes reach baryon fractions 50 per cent within 30 kpc, with a clear correlation between 𝑓 baryon and 𝑣 max . As shown by Armitage et al (2019), these high baryon fractions are the result of preferential stripping of dark matter from galaxies, while their stellar mass remains largely intact (see also Bahé et al 2019 andJoshi et al 2019). The compact, high 𝑣 max subhaloes predicted by Hydrangea are therefore most likely the result of their well-resolved, centrally concentrated stellar components being able to withstand tidal stripping in a realistic way 6 .…”

On the accretion of a new group of galaxies on to Virgo: I. Internal kinematics of nine in-falling dEs

“…In addition to the Virgo cluster, environmental mechanisms in their previous host halo (such as ram pressure stripping, tidal interactions and starvation) have possibly affected the evolution of these nine dEs before their accretion onto Virgo. This represents the condition that is commonly known as pre-processing (e.g., Gallagher & Hunter 1989;Fujita 2004;Mihos 2004;Joshi et al 2017;Han et al 2018;Joshi et al 2019). To this end, studying this group of dEs can, also address the role of pre-processing in shaping present-day properties of the "typical" dE population in clusters, as suggested by Toloba et al (2014b) and Sybilska et al (2017).…”