Stellar mass as a galaxy cluster mass proxy: application to the Dark Energy Survey redMaPPer clusters

We introduce a galaxy cluster mass observable, ${\mu }_{\star }$, based on the stellar masses of cluster members, and we present results for the Dark Energy Survey (DES) Year 1 observations. Stellar masses are computed using a Bayesian Model Averaging method, and are validated for DES data using simulations and COSMOS data. We show that ${\mu }_{\star }$ works as a promising mass proxy by comparing our predictions to X-ray measurements. We measure the X-ray temperature-${\mu }_{\star }$ relation for a total of 150 clusters matched between the wide-field DES Year 1 redMaPPer catalogue, and Chandra and XMM archival observations, spanning the redshift range $0.1<z<0.7$. For a scaling relation which is linear in logarithmic space, we find a slope of $\alpha = 0.488\pm0.043$andascatterintheX-raytemperatureatfixed$\mu_\star$of$\sigma_{{\rm ln} T_X|\mu_\star}=0.266^{+0.019}{-0.020}$ for the joint sample. By using the halo mass scaling relations of the X-ray temperature from the Weighing the Giants program, we further derive the ${\mu }_{\star }$-conditioned scatter in mass, finding $\sigma{{\rm ln} M|\mu_\star}=0.26^{+ 0.15}_{- 0.10}$. These results are competitive with well-established cluster mass proxies used for cosmological analyses, showing that ${\mu }_{\star }$ can be used as a reliable and physically motivated mass proxy to derive cosmological constraints.