Active Galactic Nuclei in Groups and Clusters of Galaxies: Detection and Host Morphology

Abstract

The incidence and properties of active galactic nuclei (AGNs) in the field, groups, and clusters can provide new information about how these objects are triggered and fueled, similar to how these environments have been employed to study galaxy evolution. We have obtained new XMM-Newton observations of seven X-ray selected groups and poor clusters with 0.02 < z < 0.06 for comparison with previous samples that mostly included rich clusters and optically selected groups. Our final sample has ten groups and six clusters in this low-redshift range (split at a velocity dispersion of σ = 500 km s −1 ). We find that the X-ray selected AGN fraction increases from−0.016 in clusters to 0.091−0.034 for the groups (85% significance), or a factor of 2, for AGN above an 0.3-8 keV X-ray luminosity of 10 41 erg s −1 hosted by galaxies more luminous than M * R + 1. The trend is similar, although less significant, for a lower-luminosity host threshold of M R = −20 mag. For many of the groups in the sample, we have also identified AGN via standard emission-line diagnostics and find that these AGNs are nearly disjoint from the X-ray selected AGN. Because there are substantial differences in the morphological mix of galaxies between groups and clusters, we have also measured the AGN fraction for early-type galaxies alone to determine if the differences are directly due to environment, or indirectly due to the change in the morphological mix. We find that the AGN fraction in early-type galaxies is also lower in clusters −0.044 for the groups (92% significance), a result consistent with the hypothesis that the change in AGN fraction is directly connected to environment.

Activity in galactic nuclei of cluster and field galaxies in the local universe

“…This finding is consistent with the results in previous studies (e.g., Popesso & Biviano 2006;Arnold et al 2009), but we further show that this anti-correlation exists for all subsamples divided by luminosity and morphology of host galaxies. One might think that the AGN fractions in this figure are somewhat large (sometimes reaches unity) compared to the results in previous studies.…”

“…5 and 9), which is consistent with previous studies (e.g. Arnold et al 2009;von der Linden et al 2010). On the other hand, the AGN fractions of late types decrease much closer to the cluster center (∼0.1−0.5r 200,cl ) than those of early types, and the AGN fractions of late-type cluster galaxies are, on average, not different from mean AGN fractions of field late types.…”

“…Since Gisler (1978) first found a lack of optical emission-line galaxies in nearby clusters, many studies have extended this comparison of the activity in galactic nuclei between cluster and field galaxies using an extensive survey data sets in the local universe (e.g., Dressler et al 1985;Popesso & Biviano 2006;Best et al 2007;Arnold et al 2009;von der Linden et al 2010;Koulouridis & Plionis 2010). For example, Arnold et al (2009) confirmed an increasing AGN fraction from cluster to group regions. One of the most interesting results in their study is that this trend remains the same even if they fix the morphology of host galaxies (e.g.…”

The Suppression of Star Formation and the Effect of the Galaxy Environment in Low-Redshift Galaxy Groups

“…However, the fraction of AGN identifiable on the basis of their optical emission lines or their X-ray properties is small for the XI sample, at the few percent level (Shen et al 2007;Bai et al 2010), so AGN contamination in the UV is generally unlikely to be important. In addition, the dependence of the AGN fraction on global environment is generally inferred to be weak (Arnold et al 2009), so we do not expect environmental variations in AGN activity to significantly impact our results. The approximate 100% completeness limit for our GALEX observations in either band can be estimated from the apparent (i.e., not extinction-corrected) magnitude histograms of all sources detected in the field of MZ 770, the group with the shortest identical exposure in FUV and NUV, and MZ 4592, the group field suffering the strongest Galactic extinction (cf.…”

The XXL Survey

“…In a scenario in which AGN are suppressed by the strong gravitational potential of massive clusters (through gas stripping, strangulation, tidal stripping, evaporation, high velocity-dispersion, etc. ), one would expect the AGN presence to rise in shallower gravitational potentials (see Arnold et al 2009;Gavazzi et al 2011;Bitsakis et al 2015) and be completely nullified within the deepest ones. In Koulouridis et al (2014), we investigated the AGN presence in two samples of poor and moderate clusters and found evidence of this anti-correlation.…”