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

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 < log(M * /M ) < 10.75 and z < 0.2 classified according to their intrinsic u * − r * colour. From single component Sérsic 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 ∼ 1 − 2 Gyr and is independent of environment, unlike that of the red and blue populations. While environment likely plays a rôle 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.

Classification and evolution of galaxies according to the dynamical state of host clusters and galaxy luminosities

“…This suggests evolution through the GV, and that S0 type is crucial for understanding the transition from late to early type objects, in agreement with recent works (e.g. Bait et al 2017;Bremer et al 2018). At the same time, the fraction of Sab decreases from SF to PAS.…”

Galaxy And Mass Assembly (GAMA): properties and evolution of red spiral galaxies

“…On the other hand, morphological transformation occurs when the star formation in a galaxy is truncated on a very short time-scale, perhaps as a result of a merger event. This is also in broad agreement with the results of Bremer et al (2018) who studied the morphological transformation of the transitional green valley galaxies (z < 0.2; 10.25 < log M * /M⊙ < 10.75) from the GAMA survey. Bremer et al (2018) find that the transition time of galaxies through the green valley is ∼ 1 − 2 Gyr, and is independent of environment.…”

“…This is also in broad agreement with the results of Bremer et al (2018) who studied the morphological transformation of the transitional green valley galaxies (z < 0.2; 10.25 < log M * /M⊙ < 10.75) from the GAMA survey. Bremer et al (2018) find that the transition time of galaxies through the green valley is ∼ 1 − 2 Gyr, and is independent of environment. Their result is in agreement with the trend seen in Fig.…”

“…In their work exploring the colours and morphology of transitional galaxies, Bremer et al (2018) also find that the green valley galaxies have significant bulge and disk components, but the transition from blue to red optical colour is driven by the colour change of the disk. Their results led these authors to suggest that star formation is quenched in the disk as the gas content is used up, or becomes less available in the period following growth of the bulge.…”

“…nearby galaxies, found in the green valley of the optical colourmagnitude space showed that the change in colours from blue to red is primarily due to the change in the colour of the disc. Bremer et al (2018) also showed that most of the green valley galaxies have significant bulges, suggesting that a strong bulge is present prior to decline in the star formation of galaxies.…”