Half-mass radii of quiescent and star-forming galaxies evolve slowly from 0 < z < 2.5: implications for galaxy assembly histories

TL;DR

This study shows that galaxy half-mass radii evolve slowly from redshift 2.5 to 0, with color gradients changing rapidly at high redshift but stabilizing later, affecting galaxy growth models.

Contribution

It provides new observational evidence that galaxy sizes grow more slowly than previously thought, especially when considering half-mass radii, and compares these findings with theoretical models.

Findings

Half-mass radii of galaxies grow slowly from z=2.5 to 0.

Color gradients evolve rapidly at high redshift but stabilize below z=1.

Quiescent galaxy growth aligns with minor merger models.

Abstract

We use high-resolution, multi-band imaging of ~16,500 galaxies in the CANDELS fields at 0 < z < 2.5 to study the evolution of color gradients and half-mass radii over cosmic time. We find that galaxy color gradients at fixed mass evolve rapidly between z~2.5 and z~1, but remain roughly constant below z~1. This result implies that the sizes of both star-forming and quiescent galaxies increase much more slowly than previous studies found using half-light radii. The half-mass radius evolution of quiescent galaxies is fully consistent with a model which uses observed minor merger rates to predict the increase in sizes due to the accretion of small galaxies. Progenitor bias may still contribute to the growth of quiescent galaxies, particularly if we assume a slower timescale for the minor merger growth model. The slower half-mass radius evolution of star-forming galaxies is in tension with cosmological simulations and semi-analytic galaxy models. Further detailed, consistent comparisons with simulations are required to place these results in context.