A comprehensive picture of baryons in groups and clusters of galaxies

Abstract

Aims. Based on XMM-Newton, Chandra, and SDSS data, we investigate the baryon distribution in groups and clusters and its use as a cosmological constraint. For this, we considered a sample of 123 systems with temperatures kT 500 = 1.0−9.0 keV, total masses in the mass range M 500 = (∼10 13 −4 × 1070 M , and redshifts 0.02 < z < 1.3. Methods. The gas masses and total masses are derived from X-ray data under the assumption of hydrostatic equilibrium and spherical symmetry. The stellar masses are based on SDSS-DR8 optical photometric data. For the 37 systems out of 123 that had both optical and X-ray data available, we investigated the gas, stellar, and total baryon mass fractions inside r 2500 and r 500 and the differential gas mass fraction within the spherical annulus between r 2500 and r 500 , as a function of total mass. For the other objects, we investigated the gas mass fraction only. Results. We find that the gas mass fraction inside r 2500 and r 500 depends on the total mass. However, the differential gas mass fraction does not show any dependence on total mass for systems with M 500 > 10 14 M . The stellar mass fraction inside r 2500 and r 500 increases towards low-mass systems more steeply than the f gas decrease with total mass. Adding the gas and stellar mass fractions to obtain the total baryonic content, we find it to increase with cluster mass, reaching the WMAP-7 value for clusters with M 500 ∼ 10 14 M . This led us to investigate the contribution of the intracluster light to the total baryon budget for lower mass systems, but we find that it cannot account for the difference observed. Conclusions. The gas mass fraction dependence on total mass observed for groups and clusters could be due to the difficulty of low-mass systems to retain gas inside the inner region (r < r 2500 ). Because of their shallower potential well, non-thermal processes are more effective in expelling the gas from their central regions outwards. Since the differential gas mass fraction is nearly constant, it provides better constraints for cosmology. Moreover, we find that the gas mass fraction does not depend on redshift at a 2σ level. Using our total f b estimates, our results imply Ω m < 0.55, and taking the highest significant estimates for f b , Ω m > 0.22.

The abundance of ultra-diffuse galaxies from groups to clusters

“…With very few exceptions (Kochanek et al 2003;van Uitert et al 2016), they all consistently measured a relation N ∝ M α , where α < 1.0. This is also consistent with the notion that the stellar mass fraction increases from clusters to group-mass haloes (Gonzalez et al 2013;Laganá et al 2013;Budzynski et al 2014;van der Burg et al 2014). In particular, Viola et al (2015) measured the relation between halo mass and apparent richness for the GAMA groups.…”

The XXL Survey

“…The stellar content of cluster galaxies and intracluster light generally represents 10−20% of the total baryonic mass (Lin & Mohr 2004;Gonzalez et al 2007;Andreon 2010Andreon , 2015Mulroy et al 2014). The overall baryon content of galaxy clusters is therefore found to be close to the Universal value (Lin et al 2003;Giodini et al 2009;Laganá et al 2013). Interestingly, these studies observed a general trend of increasing gas fraction (Sun et al 2009;Pratt et al 2009;Lovisari et al 2015) and decreasing stellar fraction (e.g.…”

The implications of the surprising existence of a large, massive CO disk in a distant protocluster

“…The higher velocities of galaxies in high redshift (proto)clusters compared to low redshift clusters 8 , for a constant mass, suggests that the impact of ram pressure stripping should be enhanced, not diminished in distant clusters. Gas at high temperatures dominate the inter-cluster medium (ICM) and the mass budget of low redshift clusters (e.g., Laganá et al 2013). The hot ICM gas has densities of ∼10 −3 to 10 −1 cm −3 , temperatures of ∼10 7 to 10 8 K, and a near unity filling factor (e.g., Sanderson et al 2009).…”