Richness Dependence of the Recent Evolution of Clusters of Galaxies

📝 Abstract

We revisit the issue of the recent dynamical evolution of clusters of galaxies using a sample of ACO clusters with z<0.14, which has been selected such that it does not contain clusters with multiple velocity components nor strongly merging or interacting clusters, as revealed in X-rays. We use as proxies of the cluster dynamical state the projected cluster ellipticity, velocity dispersion and X-ray luminosity. We find indications for a recent dynamical evolution of this cluster population, which however strongly depends on the cluster richness. Poor clusters appear to be undergoing their primary phase of virialization, with their ellipticity increasing with redshift with a rate de/dz ~ 2.5, while the richest clusters show an ellipticity evolution in the opposite direction (with de/dz ~ -1.2), which could be due to secondary infall. When taking into account sampling effects due to the magnitude-limited nature of the ACO cluster catalogue we find no significant evolution of the cluster X-ray luminosity, while the velocity dispersion increases with decreasing redshift, independent of the cluster richness, at a rate dsigma/dz ~ -1700 km/sec.

💡 Analysis

We revisit the issue of the recent dynamical evolution of clusters of galaxies using a sample of ACO clusters with z<0.14, which has been selected such that it does not contain clusters with multiple velocity components nor strongly merging or interacting clusters, as revealed in X-rays. We use as proxies of the cluster dynamical state the projected cluster ellipticity, velocity dispersion and X-ray luminosity. We find indications for a recent dynamical evolution of this cluster population, which however strongly depends on the cluster richness. Poor clusters appear to be undergoing their primary phase of virialization, with their ellipticity increasing with redshift with a rate de/dz ~ 2.5, while the richest clusters show an ellipticity evolution in the opposite direction (with de/dz ~ -1.2), which could be due to secondary infall. When taking into account sampling effects due to the magnitude-limited nature of the ACO cluster catalogue we find no significant evolution of the cluster X-ray luminosity, while the velocity dispersion increases with decreasing redshift, independent of the cluster richness, at a rate dsigma/dz ~ -1700 km/sec.

📄 Content

arXiv:0901.2035v1 [astro-ph.CO] 14 Jan 2009 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 20 November 2018 (MN LATEX style file v1.4) Richness Dependence of the Recent Evolution of Clusters of Galaxies Manolis Plionis1,2, Hrant M. Tovmassian2, Heinz Andernach3 1 National Observatory of Athens, Lofos Koufou, P.Penteli 152 36, Athens, Greece 2 Instituto Nacional de Astrof´ısica ´Optica y Electr´onica, AP 51 y 216, 72000, Puebla, Pue, Mexico 3 Argelander Inst. f¨ur Astronomie, Universit¨at Bonn, D-53121 Bonn, Germany (on leave of absence from Univ. Guanajuato, Mexico) 20 November 2018 ABSTRACT We revisit the issue of the recent dynamical evolution of clusters of galaxies using a sample of ACO clusters with z < 0.14, which has been selected such that it does not contain clusters with multiple velocity components nor strongly merging or interact- ing clusters, as revealed in X-rays. We use as proxies of the cluster dynamical state the projected cluster ellipticity, velocity dispersion and X-ray luminosity. We find in- dications for a recent dynamical evolution of this cluster population, which however strongly depends on the cluster richness. Poor clusters appear to be undergoing their primary phase of virialization, with their ellipticity increasing with redshift with a rate dǫ/dz ≃2.5 ± 0.4, while the richest clusters show an ellipticity evolution in the opposite direction (with dǫ/dz ≃−1.2 ± 0.1), which could be due to secondary infall. When taking into account sampling effects due to the magnitude-limited nature of the ACO cluster catalogue we find no significant evolution of the cluster X-ray luminosity, while the velocity dispersion increases with decreasing redshift, independent of the cluster richness, at a rate dσv/dz ≃−1700 ± 400 km s−1. Key words: galaxies: clusters: general – galaxies: evolution 1 INTRODUCTION Structure formation in CDM models proceeds by hierarchi- cal anisotropic accretion of smaller units into larger ones, along filamentary large-scale structures (e.g. Zeldovich 1970; Blumenthal et al. 1984; Shandarin & Klypin 1984). The largest gravitationally bound, or nearly so, cosmic objects are clusters of galaxies, for which indeed, there are indica- tions supporting their formation by hierarchical aggregation of smaller systems along filaments (e.g. West, Jones, & For- man 1995; Plionis & Basilakos 2002). Since the perturbation growth rate depends on different cosmological models and the dark matter content of the Universe (e.g. Peebles 1980; Lahav et al. 1991), the present dynamical state of clusters of galaxies and its rate of evolution contains important cos- mological information (e.g. Richstone, Loeb & Turner 1992; Evrard et al. 1993; Mohr et al. 1995; Suwa et al. 2003; Ho, Bahcall & Bode 2006). A variety of recent studies have attempted to charac- terize the morphological and dynamical state of groups and clusters using either optical or X-ray data (Buote & Tsai 1995, 1996; Kolokotronis et al. 2001; Jeltema et al. 2005; Hashimoto et al. 2007, and references therein) and thus to infer the evidence for their cosmological evolution (e.g. Melott, Chambers & Miller 2001; Plionis 2002; Jeltema et al. 2005; Rahman et al. 2006; Hashimoto et al. 2007). We can divide the various studies in those that have looked for indications of evolution at relatively high redshifts (e.g. Jel- tema et al. 2005; Hashimoto et al. 2007) and those that have looked for a very recent evolution (Melott et al. 2001, Plionis 2002; Rahman et al. 2006). In both types of studies there appear contradictory results on whether the dynamical state of clusters evolves significantly in the distant or recent past. Melott et al. (2001) and Plionis (2002), using the projected ellipticity, ǫ, as a proxy of the cluster dynamical state (e.g. Kolokotronis et al. 2001), found a strong recent evolution rate with dǫ/dz ≃0.7 −1 for z∼< 0.15. This appears to be in contradiction with a similar analysis for z < 0.31 of Rah- man et al. (2006) and with numerical N-body simulations (e.g. Floor et al. 2003; 2004; Ho et al. 2006) that find the recent evolution of cluster ellipticity to be much weaker. Clusters of high projected ellipticity are apparently still aggregating smaller groups and field galaxies from their sur- roundings. The increase of mass concentration and phase- mixing during virialization will tend to sphericalize the clus- ters, increase their velocity dispersion, X-ray luminosity and c⃝0000 RAS 2 Plionis, Tovmassian, Andernach temperature. Of course this simple picture is highly dis- torted by a variety of factors, like the violent merging phase, strong interactions with a dense environment, cluster rich- ness, interloper contamination, projection effects, etc. For example, the analysis of numerical simulations by Jeltema et al. (2008) shows that, using morphological criteria, less than 50% of clusters appearing relaxed in projection are truly relaxed. Therefore, in our present work we attempt to avoid sys- tematic effects, as m

This content is AI-processed based on ArXiv data.