GLASS Reveals Dual-Role Environments in Galaxy Clusters


Using the GLASS spectroscopic and very deep imaging data, Morishita et al. (2016) found that galaxy clusters are dual-role environments, which both accelerate and curtail galaxy evolution without affecting their sizes and structures.

Morishita et al. derived structural parameters of more than 3900 galaxies by using the GLASS grism spectroscopy combined  with the imaging from the Hubble Frontier Fields. The sample is unique in terms of the low masses it proves, reaching log(M*/Msun)~7.8, a factor of 10-100 lower than previous studies at the epoch of the Universe observed in this study, about 5 Gyr ago.

The paper studied galaxy size—stellar mass relations in different environments,  i.e. the cluster center (the most crowded environment in the universe) and the normal field, to study the impact of the environment on galaxy sizes. The four figures above show the size—stellar mass relations for four populations: blue and red galaxies in clusters and the field.

The origin of low-mass red galaxies is a key topic in galaxy evolution, and the target of this study. By considering structural parameters, color, and the difference in sizes between red and blue galaxies, Morishita et al. found a strong connection between low-mass red galaxies and blue galaxies of similar masses — evidence that blue galaxies are transformed by ram pressure stripping and starvation in cluster environments.

Yet, about 20% of the low-mass red galaxies could not be explained in the same scenario — that population is too old and dense (consistent with more massive log(M*/Msun) > 10 galaxies), though it also seems only to exist in cluster environments.

The authors concluded the cluster environment has two roles on low-mass galaxies evolution; one is killing galaxies (environmental quenching) without significant structural transformations; the other is an acceleration of the evolution phase, which forms high surface density galaxies more than 10 Gyr ago, spanning most masses.

For more information see Morishita et al. (2016).

The catalog used in this study will soon be available through the GLASS website.