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 lgM \la 14 M _ { \odot } , 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 \approx 0.10 dex errors for clusters of lgM \la 14 M _ { \odot } mass .