Vol. 638
4. Extragalatic astronomy

The GOGREEN Survey: A deep stellar mass function of cluster galaxies at 1.0 < z < 1.4 and the complex nature of satellite quenching

The origin of the bimodality of galaxies that separates star-forming from passive galaxies remains incompletely understood. In particular, it is not clear whether the mechanisms at play in the present-day Universe can also explain how star-formation quenched in distant galaxies. To address this question, van den Burg et al. realized the most precise measurement of the stellar mass function of galaxies in the dense environment of 11 galaxy clusters at z=1 to 1.4 using photometric measurements from the blue to the 4.5 microns bands. Surprisingly, what they find is in stark contrast to what several studies concluded from the study of nearby galaxies. These studies refer to the following two mechanisms that act separately and independently in the local Universe: a mass-independent environmental quenching and an environment-independent mass quenching. When they compare the stellar mass functions of star-forming and passive galaxies in the clusters and in the field at z=1-1.4, the authors find no signature of purely mass-independent environmental quenching. Instead galaxies in clusters appear to quench through the same processes as those in the field, simply they do so at an earlier time. They conclude that galaxies that are destined to become part of z=1-1.4 clusters start their formation “early” with respect to galaxies in the field, but they quench via a similar physical process.