Synthesizing Stellar Populations in South Pole Telescope Galaxy Clusters: I. Ages of Quiescent Member Galaxies at 0.3 < z < 1.4

• Main Authors: Khullar, Gourav, Bayliss, Matthew B., Gladders, Michael D., Kim, Keunho J., Calzadilla, Michael S, Strazzullo, Veronica, Bleem, Lindsey E., Mahler, Guillaume, McDonald, Michael, Floyd, Benjamin, Reichardt, Christian L., Ruppin, Florian, Saro, Alexandro, Sharon, Keren, Somboonpanyakul, Taweewat, Stalder, Brian, Stark, Antony A.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: arXiv 2021
• Subjects: Astrophysics of Galaxies astro-ph.GA; FOS Physical sciences; South Pole; South pole
• Online Access: https://dx.doi.org/10.48550/arxiv.2111.09318; https://arxiv.org/abs/2111.09318

Using stellar population synthesis models to infer star formation histories (SFHs), we analyse photometry and spectroscopy of a large sample of quiescent galaxies which are members of Sunyaev-Zel'dovich (SZ)-selected galaxy clusters across a wide range of redshifts. We calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < z < 1.4 using rest-frame optical spectra and the Python-based Prospector framework, from 61 clusters in the SPT-GMOS Spectroscopic Survey (0.3 < z < 0.9) and 3 clusters in the SPT Hi-z cluster sample (1.25 < z < 1.4). We analyse spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. We find that quiescent galaxies in our dataset sample a diversity of SFHs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, t$_{50}$) of $z=2.8\pm0.5$, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. We also report median age-stellar mass relations for the full sample (age of the Universe at $t_{50}$ (Gyr) = $2.52 (\pm0.04) - 1.66 (\pm0.11)$ log$_{10}(M/10^{11} M\odot))$ and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate $\sim0.75$ Gyr earlier than lower mass galaxies. We also find marginally steeper age-mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass. : 35 pages, 23 figures, 5 tables. Submitted to The Astrophysical Journal. Comments and feedback welcome