The Outer Stellar Mass of Massive Galaxies: A Simple Tracer of Halo Mass
  with Scatter Comparable to Richness and Reduced Projection Effects
  Using the weak gravitational lensing data from the Hyper Suprime-Cam Subaru
Strategic Program (HSC survey), we study the potential of different stellar
mass estimates in tracing halo mass. We consider galaxies with $\log
{M_{\star}/M_{\odot}}>11.5$ at 0.2 < z < 0.5 with carefully measured light
profiles and clusters from the redMaPPer and CAMIRA richness-based algorithms.
We devise a method (the "TopN" test) to evaluate the scatter in the halo
mass-observable relation for different tracers and inter-compare halo mass
proxies in four number density bins using stacked galaxy-galaxy lensing
profiles. This test reveals three key findings. The stellar mass based on
cModel photometry or aperture luminosity within R<30 kpc is a poor proxy of
halo mass. In contrast, the stellar mass of the outer envelope is an excellent
halo mass proxy. The stellar mass within R=[50,100] kpc, M*[50,100], has
performance comparable to the state-of-the-art richness-based cluster finders
at $\log{M_{\rm vir}/M_{\odot}}>14.0$ and could be a better halo mass tracer at
lower halo masses. Finally, using N-body simulations, we find that the lensing
profiles of massive halos selected by M*[50,100] are consistent with the
expectation for a sample without projection or mis-centering effects. On the
other hand, Richness-selected clusters display an excess at R~1 Mpc in their
lensing profiles, which may suggest a more significant impact from selection
biases. These results suggest that Mstar-based tracers have distinct advantages
in identifying massive halos, which could open up new avenues for cluster
cosmology.
