Galaxy and Mass Assembly (GAMA): Morphological transformation of galaxies across the green valley

TL;DR

This study investigates how low-redshift galaxies transition from blue to red, revealing that disk fading and pre-existing bulges drive the process, with a typical transition timescale of 1-2 Gyr independent of environment.

Contribution

It provides new insights into the morphological and photometric evolution of galaxies in the green valley, emphasizing secular disk fading and pre-existing bulges as key factors.

Findings

Green galaxies have similar K-band profiles to red galaxies, indicating similar stellar mass distributions.

Optical profiles show green galaxies are more disk-like, due to radial mass-to-light ratio variations.

Transition through the green valley takes about 1-2 Gyr, unaffected by environment.

Abstract

We explore constraints on the joint photometric and morphological evolution of typical low redshift galaxies as they move from the blue cloud through the green valley and onto the red sequence. We select GAMA survey galaxies with $10.25<{\rm log}(M_*/M_\odot)<10.75$ and $z<0.2$ classified according to their intrinsic $u^*-r^*$ colour. From single component S\'ersic fits, we find that the stellar mass-sensitive $K-$band profiles of red and green galaxy populations are very similar, while $g-$band profiles indicate more disk-like morphologies for the green galaxies: apparent (optical) morphological differences arise primarily from radial mass-to-light ratio variations. Two-component fits show that most green galaxies have significant bulge and disk components and that the blue to red evolution is driven by colour change in the disk. Together, these strongly suggest that galaxies evolve from blue to red through secular disk fading and that a strong bulge is present prior to any decline in star formation. The relative abundance of the green population implies a typical timescale for traversing the green valley $\sim 1-2$~Gyr and is independent of environment, unlike that of the red and blue populations. While environment likely plays a r\^ole in triggering the passage across the green valley, it appears to have little effect on time taken. These results are consistent with a green valley population dominated by (early type) disk galaxies that are insufficiently supplied with gas to maintain previous levels of disk star formation, eventually attaining passive colours. No single event is needed quench their star formation.