An X‐Ray and Optical Study of Matter Distribution in the Galaxy Cluster A2319

Abstract

A new analysis of velocity distribution, optical photometry and X-ray surface brightness from ROSAT PSPC data of the galaxy cluster A 2319 is presented. The temperature profile derived from ASCA data (Markevitch et al.,1996) is taken into account. A method to check the hydrostatic model in the presence of a temperature gradient is proposed. Consistency of the hydrostatic isothermal model and the explanation of the "beta-discrepancy" are discussed. Galaxy and gas density profiles of the main component A 2319A are derived, allowing for the effect of the secondary component A 2319B. The inadequacy of a polytropic model, which would produce a binding mass decrease with respect to the isothermal beta-model, is discussed. A simple interpolation of the temperature profile provides instead an increase of the binding mass and a lower baryon fraction thus mitigating the "baryon catastrophe". Assuming as typical the value f_b ~ 0.2, a comparison with the most recent estimate of Omega_b(nucl) implies for the cosmological parameter Omega_o less than 0.4.