ROSAT-SDSS Galaxy Clusters Survey. I. The Catalog and the correlation of X-ray and optical properties

TL;DR

This paper presents a comprehensive catalog of galaxy clusters from ROSAT and SDSS, analyzing their X-ray and optical properties to understand their correlation and mass-to-light ratio variations.

Contribution

It provides a uniform database of X-ray and optical properties for a large sample of galaxy clusters, and investigates the correlation between their luminosities and temperature.

Findings

Optical luminosity in the z band correlates best with X-ray luminosity.

The L_X-L_{op} correlation has a slope of 0.38, indicating a non-constant M/L ratio.

The scatter in the correlation decreases for brighter X-ray clusters.

Abstract

For a detailed comparison of the appearance of cluster of galaxies in X-rays and in the optical, we have compiled a comprehensive database of X-ray and optical properties of a sample of clusters based on the largest available X-ray and optical surveys: the ROSAT All Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS). The X-ray galaxy clusters of this RASS-SDSS catalog cover a wide range of masses, from groups of 10^{12.5} solar masses to massive clusters of 10^{15} solar masses in the redshift range from 0.002 to 0.45. The RASS-SDSS sample comprises all the X-ray selected objects already observed by the Sloan Digital Sky Survey (114 clusters). For each system we have uniformly determined the X-ray and optical properties. The total optical luminosity can be determined with a typical uncertainty of 20% with a result independent of the choice of local or global background subtraction. We found that the z band cluster luminosity determined within an aperture of 0.5 Mpc h_{70}^(-1) provides the best correlation with the X-ray luminosity with a scatter of about 60-70%. The scatter decreases to less than 40% if the correlation is limited to the bright X-ray clusters. The resulting correlation of L_X and L_{op} in the z and i bands shows a logarithmic slope of 0.38, a value not consistent with the assumption of a constant M/L. Consistency is found, however, for an increasing M/L with luminosity as suggested by other observations. We also investigated the correlation between L_{op} and the X-ray temperature obtaining the same result.