## A low-scatter survey-based mass proxy for clusters of galaxies

INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy

e-mail: stefano.andreon@brera.inaf.it

Received: 24 August 2012

Accepted: 17 October 2012

Estimates of cosmological parameters using galaxy clusters have the scatter in the observable at a given mass as a fundamental parameter. This work computes the amplitude of the scatter for a newly introduced mass proxy, the product of the cluster total luminosity times the mass-to-light ratio, usually referred as stellar mass. The analysis of 12 galaxy clusters with excellent total masses shows a tight correlation between the stellar mass, or stellar fraction, and total mass within *r*_{500} with negligible intrinsic scatter: the 90% upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is similar to the one of best-determined mass proxies, such as *Y*_{X}, i.e. the product of X-ray temperature, and gas mass. The size of the cluster sample used to determine the intrinsic scatter is small, as in previous works proposing low-scatter proxies because very accurate masses are needed to infer very small values of intrinsic scatter. Three-quarters of the studied clusters have lg*M* ≲ 14 *M*_{⊙}, which is advantageous from a cosmological perspective because these clusters are far more abundant than more massive clusters. At the difference of other mass proxies such as *Y*_{X}, stellar mass can be determined with survey data up to at least *z* = 0.9 using upcoming optical near-infrared surveys, such as DES and Euclid, or even with currently available surveys, covering however smaller solid angles. On the other end, the uncertainty about the predicted mass of a single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This is largely because the proxy itself has ≈ 0.10 dex errors for clusters of lg*M* ≲ 14 *M*_{⊙} mass.

Key words: galaxies: clusters: general / galaxies: stellar content / galaxies: luminosity function, mass function / cosmology: observations / methods: statistical / cosmological parameters

*© ESO, 2012*