The link between accretion mode and environment in radio-loud active galaxies

Abstract

The interactions between radio-loud AGN and their environments play an important rôle in galaxy and cluster evolution. Recent work has demonstrated fundamental differences between High and Low Excitation Radio Galaxies (HERGs and LERGs), and shown that they may have different relationships with their environments. In the Chandra Large Project ERA (Environments of Radio-loud AGN), we made the first systematic X-ray environmental study of the cluster environments of radio galaxies at a single epoch (z ∼ 0.5), and found tentative evidence for a correlation between radio luminosity and cluster X-ray luminosity. We also found that this relationship appeared to be driven by the LERG sub-population (Ineson et al. 2013).We have now repeated the analysis with a low redshift sample (z ∼ 0.1), and found strong correlations between radio luminosity and environment richness and between radio luminosity and central density for the LERGs but not for the HERGs. These results are consistent with models in which the HERGs are fuelled from accretion discs maintained from local reservoirs of gas, while LERGs are fuelled more directly by gas ingested from the intra-cluster medium.Comparing the samples, we found that although the maximum environment richness of the HERG environments is similar in both samples, there are poorer HERG environments in the z ∼ 0.1 sample than in the z ∼ 0.5 sample. We have therefore tentative evidence of evolution of the HERG environments. We found no differences between the LERG subsamples for the two epochs, as would be expected if radio and cluster luminosity are related.

A simulation-based analytic model of radio galaxies

“…Fig. 1 shows a comparison between a universal pressure profile with M 500 = 10 14 M and a β model with p 0 = 4 × 10 −12 Pa, r c = 30 kpc, β = 2/3 and kT = 2.3 keV, both intended to represent a poor cluster environment not uncommon for radio galaxies (Ineson et al 2015). It can be seen that the most important difference is in the pressure (therefore density) at small radii, < 1 kpc, but there are non-negligible differences at large radii too.…”

Particle content, radio-galaxy morphology, and jet power: all radio-loud AGN are not equal

“…As the demographics of the radio-loud AGN popu- Figure 3. The X-ray environment -radio luminosity relation for LERGs, from Ineson et al (2015), broken down by radio morphology. A small number of upper limits on the X-ray environmental luminosity are present, as indicated in the legend.…”

Radio Sources Associated with Optical Galaxies and Having Unresolved or Extended Morphologies (ROGUE). I. A Catalog of SDSS Galaxies with FIRST Core Identifications

“…The luminosity distance to the source, d L , has been computed using the concordant cosmology with the Hubble constant H 0 = 69.6 km/s/Mpc, Ω M = 0.286, and Ω Λ = 0.714 (Spergel et al 2007). The luminosity distance has been calculated following Hogg (1999):…”