Program: GN-2022A-Q-222

Title:Spectroscopic confirmation of a protocluster near an extremely massive quasar at z=1.47
PI:Hyunsung Jun
Co-I(s): Myungshin Im, Minhee Hyun, Jae-Woo Kim, Seong-Kook Lee, Changbom Park, John Stott, Yongmin Yoon

Abstract

Galaxy clusters are the favored environments of local massive galaxies. When these galaxies were actively accreting gas towards their supermassive black holes, galaxy mergers were likely triggering the gas accretion in group environments. The natural explanation for both findings is that z~1-2 quasars with extremely massive black holes are found in group-scale environments, yet as part of a large protocluster. We recently identified a delta=6.6 overdensity of H-alpha emitters around PG 1630+377, an extremely massive (M_BH=10^9.7 M_sun) quasar at z=1.475. Located at a projected distance 2.1 pMpc northeast of the quasar, the overdensity is the densest region in the target area of 525 square arcmin, and overlaps with the density peak of BzK color-selected galaxies. In addition, Hubble Space Telescope spectroscopy yielded another overdensity of emission-line galaxies (ELGs) in the immediate vicinity of PG 1630+377. These Mpc-scale environments are estimated to merge into a 10^14.7 M_sun cluster at present, if the spectroscopic redshifts of HAEs and BzK galaxies are within interaction distance to the ELGs. With Gemini/GMOS multi-object spectroscopy, we propose to measure the redshifts of the HAEs and BzK galaxies, in order to confirm the overdensity of photometrically selected galaxies, and assess the likelihood of multiple overdensities collapsing into a massive cluster.