The evolving disk galaxy population

TL;DR

This paper reviews the evolution of disk galaxy populations since redshift 1, highlighting their star formation activity, mass growth, and scaling relation stability over the past 8 billion years.

Contribution

It provides a simplified overview of disk galaxy evolution, emphasizing the dominant role of disk physics in star formation decline and the stability of scaling relations despite ongoing physical processes.

Findings

Disk galaxies dominate star formation at z<1.

Little change in stellar mass density since z=1.

Galaxies grow inside-out and evolve towards higher rotation velocities.

Abstract

In this contribution, I present a simplified overview of the evolution of the disk galaxy population since z=1, and a brief discussion of a few open questions. Galaxy evolution surveys have found that the disk galaxy population forms stars intensely at intermediate redshift. In particular, they dominate the cosmic star formation rate at z<1 -- the factor of ten drop in cosmic average comoving star formation rate in the last 8 Gyr is driven primarily by disk physics, not by a decreasing major merger rate. Despite this intense star formation, there has been little change in the stellar mass density in disk galaxies since z=1; large numbers of disk galaxies are being transformed into non-star-forming spheroid-dominated galaxies by galaxy interactions, AGN feedback, environmental effects, and other physical processes. Finally, despite this intense activity, the scaling relations of disk galaxies appear to evolve little. In particular, as individual galaxies grow in mass through the formation of stars, they appear to grow in radius (on average, the population grows inside-out), and they appear to evolve towards somewhat higher rotation velocity (i.e., mass is added at both small and large radii during this inside-out growth).