We introduce a galaxy cluster mass observable, {mu}, based on the stellar masses of cluster members, and we present results for the Dark Energy Survey (DES) Year 1 (Y1) 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} works as a promising mass proxy by comparing our predictions to X-ray measurements. We measure the X-ray temperature-{mu} relation for a total of 129 clusters matched between the wide-field DES Y1 redMaPPer catalogue and Chandra and XMM archival observations, spanning the redshift range 0.1<z<0.7. For a scaling relation that is linear in logarithmic space, we find a slope of {alpha}=0.488+/-0.043 and a scatter in the X-ray temperature at fixed {mu} of {sigma}lnTX|{mu}= 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}_-conditioned scatter in mass, finding {sigma}lnM|{mu}=0.26^+0.15^-0.10_. These results are competitive with well-established cluster mass proxies used for cosmological analyses, showing that {mu}_ can be used as a reliable and physically motivated mass proxy to derive cosmological constraints.

Cone search capability for table J/MNRAS/493/4591/tablea1 (Chandra clusters)

Cone search capability for table J/MNRAS/493/4591/tablea2 (XMM clusters)