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

Abstract

We searched for massive galaxy population in the known large-scale high-density structure of Ly α emitters (LAEs) at z = 2.39 near the radio galaxy 53W002 by using imaging data from B , V , i ′ , J , H , and K s bands 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 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, or V − K s > 4. In particular, the number density of the JHK s -selected galaxies with K s < 22.25 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 and J − K s > 2 are massive galaxies with M s > 10 11 M ⊙ , and their specific star formation rates (sSFRs) of 10 −11 –10 −10 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 × 10 10 M ⊙ to 10 11 M ⊙ and sSFR < 10 −11 yr −1 , as well as that of low-mass galaxies with M s = 10 9.75 –10 10 M ⊙ and various sSFRs. The massive galaxies with M s > 10 11 M ⊙ are not located at the density peaks of LAEs but widely distributed along a similar direction to the structure of LAEs over ∼15–20 comoving Mpc. On the other hand, the quiescent galaxies with sSFR < 10 −11 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.