The Evolution of Bulge-Dominated Field Galaxies from z~1 to the Present

TL;DR

This study investigates the evolution of bulge-dominated field galaxies from redshift ~1 to today, finding minimal size and velocity dispersion changes but evidence for mass-dependent star formation histories consistent with downsizing.

Contribution

It provides new insights into the size, velocity dispersion, and stellar population evolution of passive field galaxies over cosmic time, highlighting mass-dependent formation redshifts.

Findings

No significant evolution in sizes or velocity dispersions at fixed mass.

Passive field galaxies follow a steeper M/L vs. mass relation than local counterparts.

Formation redshift estimated around z=1.35, supporting downsizing.

Abstract

We analyze the stellar populations and evolutionary history of bulge-dominated field galaxies at redshifts 0.3<z<1.2 as part of the Gemini/HST Galaxy Cluster Project (GCP). High signal-to-noise optical spectroscopy from the Gemini Observatory and imaging from the Hubble Space Telescope are used to analyze a total of 43 galaxies, focusing on the 30 passive galaxies in the sample. Using the size-mass and velocity dispersion-mass relations for the passive field galaxies we find no significant evolution of sizes or velocity dispersions at a given dynamical mass between z~1 and the present. We establish the Fundamental Plane and study mass-to-light (M/L) ratios. The M/L vs. dynamical mass relation shows that the passive field galaxies follow a relation with a steeper slope than the local comparison sample, consistent with cluster galaxies in the GCP at z=0.86. This steeper slope indicates that the formation redshift is mass dependent, in agreement with "downsizing," meaning that the low mass galaxies formed their stars more recently while the high mass galaxies formed their stars at higher redshift. The zero point differences of the scaling relations for the M/L ratios imply a formation redshift of z_form=1.35(+0.10)(-0.07) for the passive field galaxies. This is consistent with the (Hdelta_A + Hgamma_A)' line index which implies a formation redshift of z_form=1.40(+0.60)(-0.18).