HOT GAS METALLICITY AND THE HISTORY OF SUPERNOVA ACTIVITY IN ELLIPTIC GALAXIES

In the near future, satellite-born X-ray spectrometers will observe equivalent widths of emission lines produced in the hot (T approximately 10(7) K) interstellar medium in individual elliptical galaxies. Abundances in the hot gas are established by stellar mass loss and supernovae. Emission-line measurements will (1) determine or put useful constraints on the stellar metallicity and its variation with galactic radius and (2) allow an evaluation of the supernova rate in these galaxies and its past variation. The time dependence of the Type Ia supernova rate in ellipticals, currently unknown, determines not only the metallicity of the present day interstellar gas, but strongly influences the interstellar gasdynamical history over the Hubble time. Metallicity and gas dynamics are strongly coupled. We describe calculations of the dynamical evolution of the hot interstellar medium in a massive elliptical galaxy assuming a variety of past variations of the supernova rate. The equivalent widths of the 6.7 keV iron line are calculated as a function of redshift and of galactic projected radius. The present-day interstellar gas in elliptical galaxies contains a fossil record of past supernova activity that can be determined from measurements of iron line equivalent widths at several projected radii in the galaxy.