A Search for Massive Galaxy Population in a Protocluster of LAEs at $z = 2.39$ near the Radio Galaxy 53W002

TL;DR

This study investigates the distribution and properties of massive galaxies in a high-density protocluster at z=2.39 near radio galaxy 53W002, revealing significant overdensities and varied star formation activities among different galaxy populations.

Contribution

It presents the first detailed analysis of massive galaxy populations in this specific protocluster, highlighting their spatial distribution and star formation states compared to field galaxies.

Findings

Significant overdensity of massive, star-forming galaxies in the protocluster.

Massive galaxies are widely distributed, not concentrated at LAE density peaks.

Quiescent galaxies avoid the LAE structure, indicating environmental effects.

Abstract

We searched for massive galaxy population in the known large-scale high-density structure of Lyman$~\alpha$ emitters (LAEs) at $z=2.39$ near the radio galaxy 53W002 by using $B,~V,~i^\prime,~J,~H,~{\rm{and}}~K_s$-bands imaging data taken with Suprime-Cam and MOIRCS on the Subaru telescope. We selected 62 protocluster member candidates by their $JHK_s$-band colors and Spectral Energy Distribution (SED) fitting analysis ($JHK_s$-selected galaxies) in our survey field of $70.2~{\rm{arcmin}}^{2}$, and compared their physical properties estimated from the SED fitting with a comparison sample in the COSMOS field. We found significant number density excesses for the $JHK_s$-selected galaxies in the 53W002 field at $K_s<22.25,~J-K_s>2,~{\rm{or}}~V-K_s>4$. In particular the number density of the $JHK_s$-selected galaxies with $K_s<22.25~{\rm{and}}~J-K_s>2$ in the 53W002 field is nine times higher than the comparison sample. Most of those with $K_s<22.25~{\rm{and}}~J-K_s>2$ are massive galaxies with $M_s>10^{11}~M_\odot$, and their sSFRs of $10^{-11}$--$10^{-10}~\rm{yr^{-1}}$ suggest that the star formation has not yet stopped completely. We also found a density excess of quiescent galaxies with $M_s=5\times10^{10}$--$10^{11}~M_\odot~{\rm{and}}~{\rm{sSFR}}<10^{-11}~\rm{yr^{-1}}$ as well as that of low-mass galaxies with $M_s=10^{9.75}$--$10^{10}~M_\odot$ and various sSFRs. The massive galaxies with $M_s>10^{11}~M_\odot$ are not located at the density peaks of LAEs, but widely distributed along the similar direction with the structure of LAEs over $\sim15$--$20$ comoving Mpc. On the other hand, the quiescent galaxies with ${\rm{sSFR}}<10^{-11}~\rm{yr^{-1}}$ clearly avoid the structure of LAEs. Our results suggest that massive galaxies also exist in this protocluster discovered by the moderate overdensity of LAEs and their star formation activities depend on location in the protocluster.