X-RAY-EMISSION AND TEMPERATURE PROFILES FOR OPTICALLY SELECTED MODELSOF ELLIPTIC GALAXIES

The main goal of this paper is to determine for a given galaxy to what extent its X-ray emission properties can restrict the class of mass m odels that is selected by its stellar dynamics. Here we focus on NGC 4 472, for which the currently available stellar dynamical data extend o ut to almost-equal-to R(e) while the X-ray data sample the region out to almost-equal-to 7R(e). We show that both the best fit stellar dynam ical model that can be proposed without invoking the presence of dark matter with M/L(B) almost-equal-to 7.2 (which is actually judged to be not acceptable in a chi2-analysis) and the model that, within a 3sigm a confidence level, contains the largest amount of dark matter in diff use form (M/L(B) almost-equal-to 47, M(D) almost-equal-to 7 M(L), r(D) almost-equal-to 7 r(L)) lead to remarkably similar X-ray emission and temperature profiles, when such emission is described by means of one standard set of steady-state cooling flow equations. We have also per formed a semi-empirical test where the density distribution of the gas is assumed (to match in detail the whole X-ray emission profile) and the temperature profiles corresponding to the various optically select ed potential wells are inferred from the condition of hydrostatic equi librium. The basic conclusion remains proved, i.e. that the predicted temperature profiles for models with or without dark matter are very s imilar to each other. If the interstellar gas is assumed to have a sol ar chemical composition and the intracluster pressure is not too high, then the predicted temperature for the models consistent with the ste llar dynamical data is close to 1 keV. The emission-weighted temperatu re is found to be in better agreement with the value of approximately 1.9 keV favored by Ginga if a sizable value of the intracluster pressu re is assumed.