The evolving relations between size, mass, surface density, and star formation in 3x10^4 galaxies since z=2

TL;DR

This study analyzes how galaxy size, mass, and surface density relate to star formation over cosmic time, revealing that both quiescent and star-forming galaxies undergo significant structural evolution since z=2, challenging existing models.

Contribution

It provides detailed observational constraints on the evolution of galaxy structural parameters and their relation to star formation, highlighting similar evolution rates for different galaxy types.

Findings

Massive quiescent galaxies have high surface densities and follow a tight mass-size relation.

Both quiescent and star-forming galaxies' sizes and densities evolve similarly over time.

Higher-mass quiescent galaxies evolve faster in structure than lower-mass ones.

Abstract

The presence of massive, compact, quiescent galaxies at z>2 presents a major challenge for theoretical models of galaxy formation and evolution. Using one of the deepest large public near-IR surveys to date, we investigate in detail the correlations between star formation and galaxy structural parameters (size, stellar mass, and surface density) from z=2 to the present. At all redshifts, massive quiescent galaxies (i.e. those with little or no star formation) occupy the extreme high end of the surface density distribution and follow a tight mass-size correlation, while star-forming galaxies show a broad range of both densities and sizes. Conversely, galaxies with the highest surface densities comprise a nearly-homogeneous population with little or no ongoing star formation, while less dense galaxies exhibit high star-formation rates and varying levels of dust obscuration. Both the sizes and surface densities of quiescent galaxies evolve strongly from z=2-0; we parameterize this evolution for both populations with simple power law functions and present best-fit parameters for comparison to future theoretical models. Higher-mass quiescent galaxies undergo faster structural evolution, consistent with previous results. Interestingly, star-forming galaxies' sizes and densities evolve at rates similar to those of quiescent galaxies. It is therefore possible that the same physical processes drive the structural evolution of both populations, suggesting that "dry mergers" may not be the sole culprit in this size evolution.