XMM-Newton/SDSS: star formation efficiency in galaxy clusters and constraints on the matter density parameter

TL;DR

This study investigates how baryon and stellar mass fractions vary with galaxy cluster mass using X-ray and optical data, revealing that star formation efficiency decreases with increasing cluster mass, impacting estimates of the universe's matter density.

Contribution

It provides new empirical evidence on the dependence of baryon and stellar mass fractions on cluster mass, combining XMM-Newton and SDSS data to refine understanding of star formation efficiency in clusters.

Findings

Total baryon fraction increases with cluster mass, reaching WMAP-7 predictions.

Stellar mass fraction decreases from 4.5% to ~1.0% as cluster mass increases.

Star formation efficiency is higher in lower mass clusters.

Abstract

It is believed that the global baryon content of clusters of galaxies is representative of the matter distribution of the universe, and can, therefore, be used to reliably determine the matter density parameter Omega_m. This assumption is challenged by the growing evidence from optical and X-ray observations that the total baryon mass fraction increases towards rich clusters. In this context, we investigate the dependence of stellar, and total baryon mass fractions as a function of mass. To do so, we used a subsample of nineteen clusters extracted from the X-ray flux limited sample HIFLUGCS that have available DR-7 Sloan Digital Sky Survey (SDSS) data. From the optical analysis we derived the stellar masses. Using XMM-Newton we derived the gas masses. Then, adopting a scaling relation we estimate the total masses. Adding the gas and the stellar mass fractions we obtain the total baryonic content that we find to increase with cluster mass, reaching 7-year Wilkinson Microwave Anisotropy Probe (WMAP-7) prediction for clusters with M_500 = 1.6 x 10^{15} M_sun. We observe a decrease of the stellar mass fraction (from 4.5% to ~1.0%) with increasing total mass where our findings for the stellar mass fraction agree with previous studies. This result suggests a difference in the number of stars formed per unit of halo mass, though with a large scatter for low-mass systems. That is, the efficiency of star formation varies on cluster scale that lower mass systems are likely to have higher star formation efficiencies. It follows immediately that the dependence of the stellar mass fraction on total mass results in an increase of the mass-to-light ratio from lower to higher mass systems. We also discuss the consequences of these results in the context of determining the cosmic matter density parameter Omega_m.