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**Session 42 - Structure and Evolution of The Universe.**

*Display session, Tuesday, June 09*

*Atlas Ballroom, *

## [42.06] A Comparison of Simple Mass Estimators for Galaxy Clusters

*T. G. Brainerd, C. M. Oaxaca (BU)*
High-resolution N-body simulations of rich clusters are used
to investigate systematic trends in the cluster masses
derived from three simple mass estimators: the weak
gravitational lensing shear field under the assumption of
circular symmetry and an isothermal cluster potential, (2)
the dynamical mass obtained from the radial velocity
dispersion under the assumption of an isothermal cluster
potential, and (3) the classical virial estimator. The
clusters were extracted from simulations of a standard cold
dark matter universe at z=0.5 and consist of order
2\times 10^5 to 3\times 10^5 particles of mass m_p =
10^10 M_ødot. The degree of agreement between the true
masses of the clusters (known a priori from the simulations)
and the masses obtained from the various estimators is a
function of physical scale.

On scales less than 0.5 Mpc, the masses obtained from the
weak lensing analysis are systematically lower than the true
masses of the clusters. Both the 2-dimensional, projected
mass and the 3-dimensional contained mass are underestimated
by \sim 35%. The masses obtained from the radial velocity
dispersion under the assumption of an isothermal potential
fare better, underestimating the projected mass by \sim
20% and the 3-dimensional mass by only \sim 10%. By
contrast, the classical virial estimator overestimates the
3-dimensional mass on this scale by as much as 80%.

On scales comparable to the ``edges'' of the clusters
(defined to be the radius inside which the mean interior
overdensity is equal to 200), the lensing analysis
underestimates the total 3-dimensional mass by \sim 10%
but overestimates the total projected mass by \sim 50%.
The isothermal dynamical mass estimator underestimates the
total 3-dimensional mass by \sim 35% and the projected
total mass by \sim 15%. The classical virial estimator
underestimates the total 3-dimensional mass of the clusters
by only \sim 10%.

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