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

Abstract

In this study we investigate 89 radio galaxies that are spectroscopically-confirmed to be members of five large scale structures 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 (HERG) 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.

The properties of radio and mid-infrared detected galaxies and the effect of environment on the co-evolution of AGN and star formation at z ∼ 1

“…The K-S tests is not conclusive between the SFG sub-sample and the overall spec-IR sample. Again, as compared to traditionally-selected RAGN hosts, at z∼1 and the same stellar mass limit, the median stellar mass is found to be 10 11.16 (Shen et al 2017). Neither high-nor lowf AGN reach this median value.…”

“…Net integration times were chosen to result in final 1σ sensitivities of about 10µJy per beam. The details of data reduction and catalogs of the SC1604, SG0023 and RXJ1821 are described in Shen et al (2017Shen et al ( , 2019. Here we describe the details of data reduction and catalogs of the rest of four fields (XLSS005, RXJ1053, RXJ0910 and RXJ1716).…”

“…We divided the overall radio-IR sample based on the estimated f AGN and radio luminosity into three sub-samples: SFGs, low-and high-f AGN , where SFGs are selected to be star formation dominated galaxies that are best fitted by f AGN < 0.1, i.e., with little to no AGN activity. We also include a radio luminosity threshold here since traditionally-selected RAGN are always found to have L 1.4GHz > 10 23.8 (Shen et al 2017, and references therein). This way, the SFG sample is considered to contain pure star-forming dominated galaxies.…”

“…The criteria and the number of galaxies are shown in Table 3. Shen et al (2017) have shown that different types of radio galaxies have different environmental preferences that suggest different scenarios. The AGN are preferentially located in the cores of clusters/groups, suggesting Bondi accretion to be the possible triggering process, while the SFG population exhibits a strong preference for intermediate regions of the clusters/groups, suggesting they could be driven by galaxygalaxy interactions and merging.…”

“…In Shen et al (2017), properties of radio galaxies and their environmental preferences in large scale structures at z ∼ 1 were studied. Radio galaxies were separated into AGN, Hybrid, and SFGs populations.…”