Properties of the X-ray emitting gas in early-type galaxies

Abstract

The authors have studied a sample of 81 E and S0 galaxies that were observed with the Einstein Observatory. Fifty-five galaxies are detected in X-rays, most of which come from a hot interstellar medium. Discrete sources may make a significant contribution to the X-ray emission for 21 of the detected galaxies with the lowest X-ray luminosity L<SUB>X</SUB> for a given optical luminosity L<SUB>B</SUB>. The authors examine the L<SUB>X</SUB> versus L<SUB>B</SUB> distribution and derive approximate values of the central electron density, central cooling time, and total mass in gas for the sample. Typical values are ≡0.1 cm<SUP>-3</SUP>, ≡5×10<SUP>6</SUP>yr, and 5×10<SUP>9</SUP>M_sun;. The short cooling times suggest the presence of cooling flows, and heating by supernovae and by gravitational processes is considered. The question of the presence of heavy halos is briefly discussed.