The brightest UV-selected galaxies in protoclusters at $z\sim 4$: Ancestors of Brightest Cluster Galaxies?

Abstract

We present the results of a survey of the brightest UV-selected galaxies in protoclusters. These proto-brightest cluster galaxy (proto-BCG) candidates are drawn from 179 overdense regions of $g$-dropout galaxies at $z\sim 4$ from the Hyper Suprime-Cam Subaru Strategic Program identified previously as good protocluster candidates. This study is the first to extend the systematic study of the progenitors of BCGs from $z\sim 2$ to $z\sim 4$. We carefully remove possible contaminants from foreground galaxies and, for each structure, we select the brightest galaxy that is at least 1 mag brighter than the fifth brightest galaxy. We select 63 proto-BCG candidates and compare their properties with those of galaxies in the field and those of other galaxies in overdense structures. The proto-BCG candidates and their surrounding galaxies have different rest-UV color $(i-z)$ distributions to field galaxies and other galaxies in protoclusters that do not host proto-BCGs. In addition, galaxies surrounding proto-BCGs are brighter than those in protoclusters without proto-BCGs. The image stacking analysis reveals that the average effective radius of proto-BCGs is $\sim 28\%$ larger than that of field galaxies. The $i-z$ color differences suggest that proto-BCGs and their surrounding galaxies are dustier than other galaxies at $z\sim 4$. These results suggest that specific environmental effects or assembly biasses have already emerged in some protoclusters as early as $z\sim 4$, and we suggest that proto-BCGs have different star formation histories than other galaxies in the same epoch.

18 pages, 11 figures, Accepted for publication in ApJ

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• The UV Luminosity Function of Protocluster Galaxies at $z\sim 4$: the Bright-end Excess and the Enhanced Star Formation Rate Density
• Implications of the Environments of Radio-detected AGN in a Complex Protostructure at z$\sim$3.3
• COSMOS2020: Identification of High-z Protocluster Candidates in COSMOS
• SILVERRUSH X: Machine Learning-Aided Selection of $9318$ LAEs at $z=2.2$, $3.3$, $4.9$, $5.7$, $6.6$, and $7.0$ from the HSC SSP and CHORUS Survey Data
• The Manhattan Suite: Accelerated galaxy evolution in the early Universe
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• Faint Quasars Live in the Same Number Density Environments as Lyman Break Galaxies at z ~ 4
• A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). IX. The Most Overdense Region at z~5 Inhabited by a Massive Radio Galaxy