Optical Luminosities and Mass--to--Light Ratios of Nearby Galaxy Clusters

TL;DR

This study analyzes 105 nearby galaxy clusters to determine their luminosities and mass-to-light ratios, finding strong correlations between luminosity and velocity dispersion, and a slight super-linear relation between mass and luminosity.

Contribution

It provides a homogeneous analysis of cluster luminosities and mass-to-light ratios, establishing new empirical relations and assessing uncertainties in these measurements.

Findings

Strong correlation between luminosity and velocity dispersion (L ∝ σ_v^{2.1--2.3})

Typical mass-to-light ratio M/L_{B_j} ≈ 250 solar units

Mass increases slightly faster than luminosity (M ∝ L^{1.2--1.3})

Abstract

We analyze a sample of 105 clusters having virial mass homogeneously estimated and for which galaxy magnitudes are available with a well defined high degree of completeness. In particular, we consider a subsample of 89 clusters with B_j band galaxy magnitudes taken from the COSMOS/UKST Southern Sky Object Catalogue. We compute cluster luminosities L_{B_j} within several clustercentric distances and within the virialization radius R_{vir}. In particular, we use the luminosity function and background counts estimated by Lumsden et al. (1997) on the Edinburgh/Durham Southern Galaxy Catalogue. We analyze the effect of several uncertainties connected to photometric data, fore/background removal, and extrapolation below the completeness limit of the photometry, in order to assess the robustness of our cluster luminosity estimates. We draw our results on the relations between luminosity and dynamical quantities from the COSMOS sample by considering mass and luminosities determined within the virialization radius. We find a very good correlation between cluster luminosity, L_{B_j}, and galaxy velocity dispersion, sigma_v, with L_{B_j} proportional to sigma_v^{2.1--2.3}. Our estimate of typical value for the mass-to-light ratio is M/L_{B_j} about 250 (in solar units). We do not find any correlation of M/L_{B_j} with cluster morphologies, i.e. Rood--Sastry and Bautz--Morgan types, and only a weak significant correlation with cluster richness. We find that mass has a slight, but significant, tendency to increase faster than the luminosity does, M proportional to L_{B_j}^{1.2--1.3}. We verify the robustness of this relation against a number of possible systematics.