Assembly of Massive Galaxies in a High-z Protocluster

TL;DR

This study investigates galaxy assembly in a high-redshift protocluster at z=3.1, revealing dense galaxy populations, hierarchical merging evidence, and correlations between galaxy properties and star formation activity.

Contribution

It provides the first wide-field deep JHK imaging analysis of the SSA22 protocluster, identifying overdense regions, multiple components in LABs, and links between galaxy properties and star formation.

Findings

Overdensity of distant red galaxies (DRGs) in the protocluster.

75% of LABs have K-band counterparts at z=3.1.

Evidence of hierarchical multiple merging in galaxy formation.

Abstract

We present the results of wide-field deep JHK imaging of the SSA22 field using MOIRCS instrument equipped with Subaru telescope. The observed field is 112 arcmin^2 in area, which covers the z=3.1 protocluster characterized by the overdensities of Ly Alpha emitters (LAEs) and Ly Alpha Blobs (LABs). The 5 sigma limiting magnitude is K_{AB} = 24.3. We extract the potential protocluster members from the K-selected sample by using the multi-band photometric-redshift selection as well as the simple color cut for distant red galaxies (DRGs; J-K_{AB}>1.4). The surface number density of DRGs in our observed fields shows clear excess compared with those in the blank fields, and the location of the densest area whose projected overdensity is twice the average coincides with the large-scale density peak of LAEs. We also found that K-band counterparts with z_{phot} = 3.1 are detected for 75% (15/20) of the LABs within their Ly Alpha halo, and the 40 % (8/20) of LABs have multiple components, which gives a direct evidence of the hierarchical multiple merging in galaxy formation. The stellar mass ofLABs correlates with their luminosity, isophotal area, and the Ly Alpha velocity widths, implying that the physical scale and the dynamical motion of Ly Alpha emission are closely related to their previous star-formation activities. Highly dust-obscured galaxies such as hyper extremely red objects (HEROs; J-K_{AB}>2.1) and plausible K-band counterparts of submillimeter sources are also populated in the high density region.