X-ray evidence for multiphase hot gas with solar abundances in the brightest elliptical galaxies

We examine whether isothermal models of the hot gas can successfully descri be the ASCA and ROSAT spectra of NGC 1399, 4472, 4636 and 5044, which are a mong the brightest elliptical galaxies in X-rays. Broad-band spectral fitti ng of the ASCA SIS and CIS data accumulated within a radius of similar to 5 arcmin for each galaxy shows that isothermal models (which also include a component for discrete sources) are unable to fit the SIS data near 1 keV, although a marginal fit for NGC 4636 is obtained if the relative abundances of several elements with respect to Fe are allowed to depart substantially from their solar values. In addition, these isothermal models typically fa il to produce the large equivalent widths of the Ka! line blends of Si and S that are measured independently of the Fe L emission lines. Two-temperature models provide substantially better broad-band fits to both the SIS and GIS data of each galaxy with the relative abundances (except f or NGC 4636) fixed at their solar values. A simple multiphase cooling flow model fits nearly as well as the two-temperature model for NGC 1399, 4472 a nd 5044. The multiphase models also predict more accurately the Si and S eq uivalent widths and the ratios of Si XIV/XIII and S XVI/XV than the isother mal models. From detailed comparison of broad-band fits to the ASCA data of these ellipticals using the MEKAL and Raymond-Smith plasma codes, we deter mine that the MEKAL plasma code las expected) is significantly more accurat e for the important energies similar to 0.7-1.4 keV, and the small residual s in the Fe L region for the best-fitting multiphase models imply that rema ining inaccuracies in the MEKAL code are insufficient to change qualitative ly the results for data of the present quality. Using various approaches, we find that the temperature gradients inferred f rom the ROSAT PSPC data of these galaxies, especially for NGC 1399 and 5044 , are inconsistent with the isothermal models obtained from fitting the ASC A data within a single aperture, but are very consistent with the multiphas e models. Therefore, models that assume isothermal gas within r similar to 5 arcmin are inconsistent with the ASCA and ROSAT PSPC data of these ellipt ical galaxies. Simple two-temperature models and multiphase cooling flows p rovide much better descriptions of these data sets with Fe abundances of si milar to 1-2 solar and (except for NGC 4636) relative abundances fixed at t heir solar values. We discuss the implications of these nearly solar abunda nces.