AChandraSurvey of Early‐Type Galaxies. I. Metal Enrichment in the Interstellar Medium

We present the first in a series of papers studying the X-ray properties of28 early type galaxies spanning ~3 orders of magnitude in L_x. We reportemission-weighted constraints for Fe, O, Ne, Mg, Si, S and Ni. We find noevidence of the very sub-solar Z_Fe historically reported, confirming a trendin recent X-ray observations of bright galaxies and groups, nor do we find Z_Fecorrelates with L_x. In general we find no evidence for multi-phase ISM,indicating multi-temperature fits found with ASCA were due to temperaturegradients Chandra can resolve. We compare the stellar Z_Fe, estimated fromsimple stellar population model fits, to Z_Fe(ISM). Excepting one possibleoutlier we find no evidence that the gas is much more metal-poor than the starsand, in a few systems Z_Fe(ISM) is higher. In general the two exhibit similarZ_Fe, which is inconsistent with both galactic wind models and recenthierarchical chemical enrichment simulations. Adopting standard SNIa and SNIImetal yields our abundance ratio constraints imply 66+/-11% of the Fe withinthe ISM was produced in SNIa, similar to the Solar neighbourhood and implyingsimilar enrichment histories for the ISM in a spiral and in ellipticalgalaxies. Although these values are sensitive to systematic uncertainties inthe SN yields, they are in good agreement with observations of more massivesystems, indicating remarkable homology in the enrichment process operatingfrom cluster scales to low-to-intermediate L_x galaxies. The data alsouniformly exhibit the low Z_O/Z_Mg abundance ratios which have been reported insome other systems. This is inconsistent with metal-production calculations inSNII and may indicate an additional source of enrichment, such as PopulationIII hypernovae.(abridged)Comment: Accepted for publication in the Astrophysical Journal. 23 pages, 6 figures. Mostly minor changes to match published version. Expanded correlation discussion. Conclusions unchange