On the Decline of Star Formation during the Evolution of Galaxies

TL;DR

This paper investigates why star formation rates decline in evolving galaxies, finding that the decrease in cold gas density and outward movement of star-forming regions lead to reduced star formation, supporting inside-out galaxy growth.

Contribution

It demonstrates that the decline in star formation is due to decreasing cold gas density caused by the outward migration of star-forming regions in disk galaxies.

Findings

Cold gas density decreases over time.

Star-forming regions move outward to larger radii.

Supports inside-out growth model of disk galaxies.

Abstract

Cosmological simulations predict that during the evolution of galaxies, the specific star formation rate continuously decreases. In a previous study we showed that generally this is not caused by the galaxies running out of cold gas but rather a decrease in the fraction of gas capable of forming stars. To investigate the origin of this behavior, we use disk galaxies selected from the cosmological hydrodynamical simulation Magneticum Pathfinder and follow their evolution in time. We find that the mean density of the cold gas regions decreases with time. This is caused by the fact that during the evolution of the galaxies, the star-forming regions move to larger galactic radii, where the gas density is lower. This supports the idea of inside-out growth of disk galaxies.