Star formation concentration as a tracer of environmental quenching in action: a study of the eagle and c-eagle simulations

Abstract

We study environmental quenching in the Eagle/C-Eagle cosmological hydrodynamic simulations over the last 11 Gyr (i.e. z = 0 − 2). The simulations are compared with observations from the SAMI Galaxy Survey at z = 0. We focus on satellite galaxies in galaxy groups and clusters ($10^{12}\, \rm M_{\odot }$ ≲ M200 < $3 \times 10^{15}\, \rm M_{\odot }$). A star-formation concentration index [C-index =log10(r50, SFR/r50, rband)] is defined, which measures how concentrated star formation is relative to the stellar distribution. Both Eagle/C-Eagle and SAMI show a higher fraction of galaxies with low C-index in denser environments at z = 0 − 0.5. Low C-index galaxies are found below the SFR-M⋆ main sequence (MS), and display a declining specific star formation rate (sSFR) with increasing radii, consistent with “outside-in” environmental quenching. Additionally, we show that C-index can be used as a proxy for how long galaxies have been satellites. These trends become weaker at increasing redshift and are absent by z = 1 − 2. We define a quenching timescale tquench as how long it takes satellites to transition from the MS to the quenched population. We find that simulated galaxies experiencing “outside-in” environmental quenching at low redshift (z = 0 ∼ 0.5) have a long quenching timescale (median tquench > 2 Gyr). The simulated galaxies at higher redshift (z = 0.7 ∼ 2) experience faster quenching (median tquench < 2Gyr). At z ≳ 1 − 2 galaxies undergoing environmental quenching have decreased sSFR across the entire galaxy with no “outside-in” quenching signatures and a narrow range of C-index, showing that on average environmental quenching acts differently than at z ≲ 1.

Globular Clusters in Early-Type Galaxies

“…Although, ★ E-mail: dforbes@swin.edu.au it is important to note that at higher stellar masses, this trend inverts. Galaxies may also be subject to tidal stripping, resulting in a galaxy with a reduced halo mass, at a given stellar mass, since DM material is preferentially removed before stars (Wang et al 2023). Thus passive galaxies of low stellar mass and/or those tidally stripped might be expected to have lower mean halo masses at the stellar masses typical of UDGs.…”