X‐ray spectral analysis of elliptical galaxies from ASCA : the Fe abundance in a multiphase medium

We present spectral analysis of ASCA data of 17 elliptical and three lenticular galaxies most of which have high L x / L B . Single‐temperature models ( mekal and Raymond–Smith) give unacceptable fits (χ 2 red  > 1.5 in most cases and, in agreement with previous studies, give very subsolar abundances, 〈  Z 〉 = 0.19 ± 0.12 Z⊙ ( mekal ). The spectra for approximately half the sample are fitted better by a cooling‐flow model, which in three cases gives a substantially better fit. The abundances derived from the cooling‐flow model are also significantly larger, 〈 Z 〉 = 0.6 ± 0.5 Z⊙. We empirically tested the reliability of the plasma codes in the Fe L region and found no evidence for serious problems with the determined temperatures and abundances.  Two‐temperature models give substantially better fits that are formally acceptable (χ 2 red  ∼ 1.0) in all but a few cases. The highest signal‐to‐noise ratio galaxies (which also have highest L x / L B ) have fitted temperatures < 2 keV for both components consistent with each being distinct phases of hot gas. The lowest signal‐to‐noise ratio galaxies (which also have lowest L x / L B ) generally have a hot component with temperature, T H  ≳ 5 keV, which is consistent with emission from discrete sources. (We discuss the origin of these two components from analysis of L x  −  L B and L x / L B .) The abundances of these two‐temperature models are approximately solar, 〈 Z 〉 = 0.9 ± 0.7 Z⊙ ( mekal ), consistent with a recent multiphase model for the evolution of hot gas in ellipticals. Finally, for several galaxies we find evidence for absorption in excess of the Galactic value and discuss its implications.