Interpreting the Evolution of the Size - Luminosity Relation for Disk Galaxies from Redshift 1 to the Present

TL;DR

This study uses high-resolution cosmological simulations to analyze how disk galaxy sizes and luminosities evolve from redshift 1 to the present, revealing mass-dependent growth patterns and surface brightness dimming consistent with observations.

Contribution

It introduces a method to measure disk sizes directly from simulated images, avoiding assumptions about light following mass, and provides new insights into the mass-dependent evolution of galaxy properties over time.

Findings

Simulated disks match observed size-magnitude relations at z=0 and z=1.

Galaxies with M* > 10^9 M_sun grow more in size than in luminosity since z=1.

Dwarf galaxies tend to evolve more in luminosity than size.

Abstract

A sample of very high resolution cosmological disk galaxy simulations is used to investigate the evolution of galaxy disk sizes back to redshift 1 within the Lambda CDM cosmology. Artificial images in the rest frame B band are generated, allowing for a measurement of disk scale lengths using surface brightness profiles as observations would, and avoiding any assumption that light must follow mass as previous models have assumed. We demonstrate that these simulated disks are an excellent match to the observed magnitude - size relation for both local disks, and for disks at z=1 in the magnitude/mass range of overlap. We disentangle the evolution seen in the population as a whole from the evolution of individual disk galaxies. In agreement with observations, our simulated disks undergo roughly 1.5 magnitudes/arcsec^2 of surface brightness dimming since z=1. We find evidence that evolution in the magnitude - size plane varies by mass, such that galaxies with M* > 10^9 M_sun undergo more evolution in size than luminosity, while dwarf galaxies tend to evolve potentially more in luminosity. The disks grow in such a way as to stay on roughly the same stellar mass - size relation with time. Finally, due to an evolving stellar mass - SFR relation, a galaxy at a given stellar mass (or size) at z=1 will reside in a more massive halo and have a higher SFR, and thus a higher luminosity, than a counterpart of the same stellar mass at z=0.