Journal ArticleThe stellar mass function of quiescent galaxies in 2 &lt; <i>z</i> &lt; 2.5 protoclustersEdward, Adit H; Balogh, Michael L; Bahé, Yannick M; Cooper, M C; Hatch, Nina A; Marchioni, Justin; Muzzin, Adam; Noble, Allison; Rudnick, Gregory H; Vulcani, Benedetta; Wilson, Gillian; De Lucia, Gabriella; Demarco, Ricardo; Forrest, Ben; Hirschmann, Michaela; Castignani, Gianluca; Cerulo, Pierluigi; Finn, Rose A; Hewitt, Guillaume; Jablonka, Pascale; Kodama, Tadayuki; Maurogordato, Sophie; Nantais, Julie; Xie, Lizhi<title>ABSTRACT</title> <p>We present an analysis of the galaxy stellar mass function (SMF) of 14 known protoclusters between 2.0 &lt; z &lt; 2.5 in the COSMOS field, down to a mass limit of 109.5 M⊙. 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 ∼2σ. There is no strong evidence for a dominant population of quiescent galaxies at any mass, with a fraction &lt;15 per cent at 1σ confidence for galaxies with log M*/M⊙ &lt; 10.5. We compare our results with a sample of galaxy groups at 1 &lt; z &lt; 1.5, and demonstrate that a significant amount of environmental quenching must take place between these epochs, increasing the relative abundance of high-mass ($\rm M_{\ast } \gt 10^{10.5} {\rm M}_{\odot }$) quiescent galaxies by a factor ≳ 2. However, we find that at lower masses ($\rm M_{\ast } \lt 10^{10.5} {\rm M}_{\odot }$), no additional environmental quenching is required.</p>Monthly Notices of the Royal Astronomical Society2023-11-2710494087Monthly Notices of the Royal Astronomical Society52738598 to 86170035-8711https://doi.org/10.1093/mnras/stad37512206473; 2347348National Science Foundation