A comprehensive picture of baryons in groups and clusters of galaxies^⋆

¹ IAG, USP, R. do Matão 1226, 05508-090 São Paulo/SP, Brazil
e-mail: tflagana@astro.iag.usp.br
² UPMC – CNRS, UMR7095, Institut d’Astrophysique de Paris 98bis Bd Arago, 75014 Paris, France
³ H. H. Wills Physics Laboratory, University of Bristol, Tyndall Ave, Bristol BS8 1TL, UK
⁴ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Received: 20 September 2012
Accepted: 22 April 2013

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 kT₅₀₀ = 1.0−9.0 keV, total masses in the mass range M₅₀₀ = (~10¹³-4 × 10¹⁵)h₇₀^-1 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 r₂₅₀₀ and r₅₀₀ and the differential gas mass fraction within the spherical annulus between r₂₅₀₀ and r₅₀₀, 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 r₂₅₀₀ and r₅₀₀ depends on the total mass. However, the differential gas mass fraction does not show any dependence on total mass for systems with M₅₀₀ > 10¹⁴  M_⊙. The stellar mass fraction inside r₂₅₀₀ and r₅₀₀ 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 M₅₀₀ ~ 10¹⁴  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 < r₂₅₀₀). 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.