  This presentation is a Moriond version of our recent paper (Kravtsov,
Vikhlinin & Nagai astro-ph/0603205) where we discussed X-ray proxies for the
total cluster mass, including the spectral temperature (Tx), gas mass measured
within r500 (Mg), and the new proxy, Yx, which is a simple product of Tx and
Mg. We use mock Chandra images constructed for a sample of clusters simulated
with high resolution in the concordance LambdaCDM cosmology. The simulated
clusters exhibit tight correlations between the considered observables and
total mass. The normalizations of the M500-Tx, Mg-Tx, and M500-Yx relations
agree to better than =~ 10-15% with the current observational measurements of
these relations. Our results show that Yx is the best mass proxy with a
remarkably low scatter of only =~ 5-7% in M500 for a fixed Yx, at both low and
high redshifts and regardless of whether clusters are relaxed or not. In
addition, we show that redshift evolution of the Yx-M500 relation is close to
the self-similar prediction, which makes Yx a very attractive mass indicator
for measurements of the cluster mass function from X-ray selected samples.
