Implications of the Environments of Radio-detected Active Galactic Nuclei in a Complex Protostructure at z ~ 3.3

The relationship between environment and galaxy evolution remains an open question in the high-redshift universe when clusters are in their early stages, termed “protoclusters”. The past decade has been witness to immense progress in the searching and understanding of the protocluster both from a theoretical and observational perspective. Among these studies, I introduce the Charting Cluster Construction with the VIMOS Ultra-Deep Survey (VUDS) and ORELSE (C3VO) survey, an ongoing spectroscopy campaign with both DEIMOS/Keck and MOSFIRE/Keck, to provide a nearly complete mapping of the five protoclusters at 2 < z < 5 detected in the VIMOS Ultra-Deep Survey (VUDS) fields

In this poster, I focus on one of the protocluster PCl J0227-0421 at z=3.3 and the two radio-detect AGNs (RAGNs) newly found in and around it. The three-dimensional overdensity map around this protocluster was revised using new spectroscopic observations obtained from the Keck/MOSFIRE as part of the C3VO survey and previous spectroscopic data obtained as part of the VIMOS-Very Large Telescope Deep Survey and VUDS. This protocluster is actually embedded in a complex proto-structure that has an estimated total mass of \(\sim2.6\times10^{15}M_\odot\) and contains several overdensity peaks. 

This is the first time that two RAGNs at low luminosity (\(L_{1.4GHz} \sim10^{25} W\ Hz^{-1}\)) have been found and studied within a high-redshift protostructure. Both RAGNs are hosted by either the brightest or the most massive galaxies in this proto-strucutre, thus being by definition the progenitor of BCGs. However, their hosts show extreme differences in color, indicating that they are dominated by different stellar populations or/and have experienced different evolutionary paths. Meanwhile, one of the RAGN, named "radio-BCG", also the most massive galaxy, resides in the least massive peak in this proto-structure. This is an example of pre-processing that it has formed a considerable fraction of its stellar mass before even entering the main peak. In addition, examining their surrounding environments, neither are coincident with the most locally overdense regions of the proto-structure, lacking any nearby bright companions. Thus, we propose a scenario where merging might have already happened in both cases, which lowered the local density of their surrounding area and boosted their stellar mass.