The evolution of galaxy sizes

TL;DR

This study investigates how galaxy sizes vary with environment and age in the local universe, comparing with high-redshift data to understand size evolution over cosmic time.

Contribution

It provides new insights into the environmental dependence of galaxy sizes and quantifies the mild size evolution of individual galaxies from high to low redshift.

Findings

Galaxies similar to high-z compact ones are more common in clusters.

Older galaxies tend to have smaller sizes at fixed mass.

Size evolution of individual galaxies since high-z is approximately a factor of 1.6.

Abstract

We present a study of galaxy sizes in the local Universe as a function of galaxy environment, comparing clusters and the general field. Galaxies with radii and masses comparable to high-z massive and compact galaxies represent 4.4% of all galaxies more massive than 3 X 10^{10} M_sun in the field. Such galaxies are 3 times more frequent in clusters than in the field. Most of them are early-type galaxies with intermediate to old stellar populations. There is a trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass. We show the relation between size and luminosity-weighted age for galaxies of different stellar masses and in different environments. We compare with high-z data to quantify the evolution of galaxy sizes. We find that, once the progenitor bias due to the relation between galaxy size and stellar age is removed, the average amount of size evolution of individual galaxies between high- and low-z is mild, of the order of a factor 1.6.