The stellar mass function of quiescent galaxies in 2 < z < 2.5 protoclusters

Abstract

We present an analysis of the galaxy stellar mass function (SMF) of 14 known protoclusters between $2.0<z<2.5$ in the COSMOS field, down to a mass limit of $10^{9.5}$ M${}_{\odot }$. We use existing photometric redshifts with a statistical background subtraction, and consider star-forming and quiescent galaxies identified from $(NUV-r)$ and $(r-J)$ colours separately. Our fiducial sample includes galaxies within 1 Mpc of the cluster centres. The shape of the protocluster SMF of star-forming galaxies is indistinguishable from that of the general field at this redshift. Quiescent galaxies, however, show a flatter SMF than in the field, with an upturn at low mass, though this is only significant at $\sim 2\ddot{I}ƒ$. There is no strong evidence for a dominant population of quiescent galaxies at any mass, with a fraction of $<15\%$ at $1\ddot{I}ƒ$ confidence for galaxies with log$M_{\ast }/M_{\odot }<10.5$. We compare our results with a sample of galaxies groups at $1<z<1.5$, and demonstrate that a significant amount of environmental quenching must take place between these epochs, increasing the relative abundance of high-mass ($\mathrm{M}>10^{10.5}{\mathrm{M}}_{\odot }$) quiescent galaxies by a factor of $\gtrsim$ 2. However, we find that at lower masses ($\mathrm{M}<10^{10.5}{\mathrm{M}}_{\odot }$), no additional environmental quenching is required.

23 pages, 22 figures. Accepted for publication in MNRAS