Center-Excised X-ray Luminosity as an Efficient Mass Proxy for Future
  Galaxy Cluster Surveys
  The cosmological constraining power of modern galaxy cluster catalogs can be
improved by obtaining low-scatter mass proxy measurements for even a small
fraction of sources. In the context of large upcoming surveys that will reveal
the cluster population down to the group scale and out to high redshifts,
efficient strategies for obtaining such mass proxies will be valuable. In this
work, we use high-quality weak lensing and X-ray mass estimates for massive
clusters in current X-ray selected catalogs to revisit the scaling relations of
the projected, center-excised X-ray luminosity ($L_{ce}$), which previous work
suggests correlates tightly with total mass. Our data confirm that this is the
case, with $L_{ce}$ having an intrinsic scatter at fixed mass comparable to
that of gas mass, temperature or $Y_X$. Compared to these other proxies,
however, $L_{ce}$ is less susceptible to systematic uncertainties due to
background modeling, and can be measured precisely with shorter exposures. This
opens up the possibility of using $L_{ce}$ to estimate masses for large numbers
of clusters discovered by new X-ray surveys (e.g. eROSITA) directly from the
survey data, as well as for clusters discovered at other wavelengths, with
relatively short follow-up observations. We describe a simple procedure for
making such estimates from X-ray surface brightness data, and comment on the
spatial resolution required to apply this method as a function of cluster mass
and redshift. We also explore the potential impact of Chandra and XMM-Newton
follow-up observations over the next decade on dark energy constraints from new
cluster surveys.
