The role of AGN activity in the building up of the BCG at z~1.6

TL;DR

This study investigates the central region of a massive galaxy cluster at z~1.6, revealing multiple active galactic nuclei (AGN) and merging galaxy groups, which suggest AGN activity influences the formation of the Brightest Cluster Galaxy (BCG).

Contribution

First detailed multi-wavelength analysis of the core of a z~1.6 galaxy cluster showing multiple AGN and merging activity linked to BCG formation.

Findings

Identification of two galaxy groups with merging signatures.

Detection of three obscured and luminous AGN in the cluster core.

Evidence that AGN activity may influence BCG assembly within 2.5 Gyrs.

Abstract

XDCPJ0044.0-2033 is one of the most massive galaxy cluster at z~1.6, for which a wealth of multi-wavelength photometric and spectroscopic data have been collected during the last years. I have reported on the properties of the galaxy members in the very central region (~70kpc x 70kpc) of the cluster, derived through deep HST photometry, SINFONI and KMOS IFU spectroscopy, together with Chandra X-ray, ALMA and JVLA radio data. In the core of the cluster, we have identified two groups of galaxies (Complex A and Complex B), seven of them confirmed to be cluster members, with signatures of ongoing merging. These galaxies show perturbed morphologies and, three of them show signs of AGN activity. In particular, two of them, located at the center of each complex, have been found to host luminous, obscured and highly accreting AGN (lambda=0.4-0.6) exhibiting broad Halpha line. Moreover, a third optically obscured type-2 AGN, has been discovered through BPT diagram in Complex A. The AGN at the center of Complex B is detected in X-ray while the other two, and their companions, are spatially related to radio emission. The three AGN provide one of the closest AGN triple at z>1 revealed so far with a minimum (maximum) projected distance of 10 kpc (40 kpc). The discovery of multiple AGN activity in a highly star-forming region associated to the crowded core of a galaxy cluster at z~1.6, suggests that these processes have a key role in shaping the nascent Brightest Cluster Galaxy, observed at the center of local clusters. According to our data, all galaxies in the core of XDCPJ0044.0-2033 could form a BCG of Mstar ~ 10^{12} Msun hosting a BH of 2 x 10^{8}-10^{9}Msun, in a time scale of the order of 2.5 Gyrs.