``The Sunyaev-Zel'dovich Effect in Abell 370''
We present interferometric measurements of the Sunyaev-Zel'dovich (SZ) effect
towards the galaxy cluster Abell 370. These measurements, which directly
probe the pressure of the cluster's gas, show the gas distribution to be
strongly aspherical, as
do the x-ray and gravitational lensing observations.
We calculate the cluster's gas mass fraction in two ways. We first compare
the gas mass derived
from the SZ measurements to the lensing-derived
gravitational mass near the critical lensing radius. We also calculate
the gas mass fraction from the SZ data by deprojecting the
three-dimensional gas density
distribution and deriving the total mass under the assumption that the
gas is in hydrostatic equilibrium (HSE).
We test the assumptions in the HSE method by comparing the total cluster
mass implied by the two methods and find that they agree within the
errors of the measurement. We discuss the possible systematic errors
in the gas mass fraction measurement and the constraints it places on
the matter density parameter, OmegaM.