CODEX: Role of velocity substructure in the scaling relations of galaxy clusters

Abstract

Context. The use of galaxy clusters as cosmological probes relies on a detailed understanding of their properties. They define cluster selection and ranking linked to a cosmologically significant cluster mass function. Previous studies have employed small samples of clusters, concentrating on achieving the first calibrations of cluster properties with mass, while the diversity of cluster properties has been revealed via detailed studies. Aims. The large spectroscopic follow-up on the CODEX cluster sample with SDSS and NOT enables a detailed study of hundreds of clusters, lifting the limitations of previous samples. We aim to update the spectroscopic cluster identification of CODEX by running the spectroscopic group finder on the follow-up spectroscopy results and connecting the dynamical state of clusters to their scaling relations. Methods. We implemented a reproducible spectroscopic membership determination and cleaning procedures, based on the redMaPPer membership, running the spectroscopic group finder on the follow-up spectroscopy results and cleaning the membership for spectroscopic outliers. We applied the Anderson-Darling test for velocity substructure and analysed its influence on the scaling relations. We also tested the effect of the X-ray-to-optical centre offset on the scaling relations. Results. We report on the scaling relations between richness, X-ray luminosity, and velocity dispersion for a complete sample of clusters with at least 15 members. Clusters with velocity substructure exhibit enhanced velocity dispersion for a given richness and are characterized by 2.5 times larger scatter. Clusters that have a strong offset in X-ray-to-optical centres have comparable scaling relations as clusters with substructure. We demonstrate that there is a consistency in the parameters of the scaling relations for the low- and high-richness galaxy clusters. Splitting the clusters by redshift, we note a decrease in scatter with redshift in all scaling relations. We localize the redshift range where a high scatter is observed to z < 0.15, which is in agreement with the literature results on the scatter. We note that the increase in scatter for both high- and low-luminosity clusters is z < 0.15, suggesting that both cooling and the resulting active galactic nucleus feedback are at the root of this scatter.

Galaxy Groups as the Ultimate Probe of AGN Feedback

“…The properties of the IGrM predicted by modern hydrodynamical simulations implementing different feedback models strongly vary from one simulation to another (see Figure 2). Calibrating the feedback model against high-fidelity measurements of IGrM properties is therefore a key step toward creating a unified model of energy injection by AGN in galaxy evolution models; • To advance our understanding of IGrM properties, we were recently awarded the XMM-Newton Group AGN Project (X-GAP), a large program on XMM-Newton targeting a sample of 49 galaxy groups selected by cross-matching SDSS FoF catalogues with weak RASS extended sources (see Figure 3; [56]). In Appendix A, we provide a master table describing the selected sources and an XMM-Newton image gallery.…”

“…While spectroscopic group catalogues are much cleaner than their photometric equivalent, they can still be affected by projection effects. For instance, testing their algorithm on mock data, Robotham et al [12] estimate that 20-30% of the groups detected with at least five group members are not bona fide group-scale halos, but are rather unvirialised systems composed of several smaller halos (see also [56]). Conversely, group selection based on X-ray surveys such as the ROSAT all-sky survey (RASS, [50,57]) or eR,OSITA [58], yields group samples that are very pure, since the selection is based on the presence of a virialised IGrM.…”

“…Given our goal of selecting a highly pure and unbiased sample, following Damsted et al [56] we attempted to combine the best features of both selection methods by cross-correlating galaxy groups selected from optical spectroscopic surveys with the presence of faint, extended X-ray sources. Starting from the SDSS FoF group catalogue of Tempel et al [19], we selected galaxy groups with a minimum of eight spectroscopic members, and cross-correlated their position with diffuse sources selected from the RASS data.…”

“…Moreover, the cross-correlation with SDSS groups provides a wealth of supporting optical data, in particular, redshifts, velocity dispersions, star formation rates, and stellar masses. For more details on the selection of the parent sample, we refer the reader to Damsted et al [56].…”

“…Figure3. X-GAP group selection cross-matching extended sources detected in RASS with SDSS spectroscopic galaxy groups[56]. The plot shows the RASS X-ray luminosity and the corresponding mass estimated through a luminosity-mass relation as a function of the source redshift.…”