The properties of radio galaxies and the effect of environment in large-scale structures at z ∼ 1

November 2017 • 2017MNRAS.472..998S

Authors • Shen, Lu • Miller, Neal A. • Lemaux, Brian C. • Tomczak, Adam R. • Lubin, Lori M. • Rumbaugh, Nicholas • Fassnacht, Christopher D. • Becker, Robert H. • Gal, Roy R. • Wu, Po-Feng. • Squires, Gordon

Abstract • In this study, we investigate 89 radio galaxies that are spectroscopically confirmed to be members of five large-scale structures (LSSs) in the redshift range of 0.65 ≤ z ≤ 0.96. Based on a two-stage classification scheme, the radio galaxies are classified into three sub-classes: active galactic nucleus (AGN), Hybrid, and star-forming galaxy (SFG). We study the properties of the three radio sub-classes and their global and local environmental preferences. We find AGN hosts are the most massive population and exhibit quiescence in their star formation activity. The SFG population has a comparable stellar mass to those hosting a radio AGN but are unequivocally powered by star formation. Hybrids, though selected as an intermediate population in our classification scheme, were found in almost all analyses to be a unique type of radio galaxies rather than a mixture of AGN and SFGs. They are dominated by a high-excitation radio galaxy population. We discuss environmental effects and scenarios for each sub-class. AGN tend to be preferentially located in locally dense environments and in the cores of clusters/groups, with these preferences persisting when comparing to galaxies of similar colour and stellar mass, suggesting that their activity may be ignited in the cluster/group virialized core regions. Conversely, SFGs exhibit a strong preference for intermediate-density global environments, suggesting that dusty starbursting activity in LSSs is largely driven by galaxy-galaxy interactions and merging.

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Gordon Squires

Senior Scientist