Weak Lensing Calibrated M-T Scaling Relation of Galaxy Groups in the
  COSMOS Field
  The scaling between X-ray observables and mass for galaxy clusters and groups
is instrumental for cluster based cosmology and an important probe for the
thermodynamics of the intracluster gas. We calibrate a scaling relation between
the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups
in the COSMOS field, combined with 55 higher mass clusters from the literature.
The COSMOS data includes HST imaging and redshift measurements of 46 source
galaxies per square arcmin, enabling us to perform unique weak lensing
measurements of low mass systems. Our sample extends the mass range of the
lensing calibrated M-T relation an order of magnitude lower than any previous
study, resulting in a power-law slope of 1.48$^{+0.13}_{-0.09}$. The slope is
consistent with the self-similar model, predictions from simulations, and
observations of clusters. However, X-ray observations relying on mass
measurements derived under the assumption of hydrostatic equilibrium have
indicated that masses at group scales are lower than expected. Both simulations
and observations suggest that hydrostatic mass measurements can be biased low.
Our external weak lensing masses provides the first observational support for
hydrostatic mass bias at group level, showing an increasing bias with
decreasing temperature and reaching a level of 30-50% at 1 keV.
