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A. E. Athey, J. N. Bregman , J. A. Irwin (University of Michigan)
As part of our ongoing study of the interstellar medium(ISM) in early-type galaxies, we are continuing to develop an observation-based model of the evolution and properties of the gas. Through a combined study of several key points in the ISM lifecycle, we hope to shed new insight into the current models of ISM origin, metal enrichment and evolutionary fate. We have determined the injection rate of mass into the ISM by observing dust from AGB stellar mass loss in the near-infrared with ISO. Typical injection rates are on the order of half a solar mass per year in general agreement with theoretical stellar evolutionary models with some unexplained deviations. We have also observed the cool (T~3000K) component of the ISM through optical lines typically associated with H II regions. These observations suggests a modest enrichment history with metallicities around half of solar. In a related study, we identified the [O VI] doublet in FUSE data, indicative of gas cooling at temperatures of 3x105K. These data confirm the presence of a cooling flow and provide a thermal link between the optical data and the hot (T~106-7K) diffuse X-ray component. Recent X-ray satellite missions have observed this diffuse ISM component to have very low metallicities, on the order of a tenth solar when fit with the simplest models. The metal content can be increased with a two-temperature model fit to the data, but the validity of these models are still seeking observational support. In addition, since the optical emission line gas morphology is similar to that of the X-ray diffuse emission, it is expected that both are tracing the same gas. However, discrepancies in the metallicities between these populations could lead to a revised link between these hot and cool components. In an attempt to address some of these issues, we have analyzed all of the early-type gas-rich galaxies in the Chandra archive to date and report on the metallicity and environmental properties of the diffuse X-ray component of the ISM. The high spectral resolution of Chandra allows for better spectral fitting to the iron features, revealing more accurate metallicities. In addition, the excellent spatial resolution aids in the removal of point sources, further isolating the diffuse component.
The author(s) of this abstract have provided an email address for comments about the abstract: alex@astro.lsa.umich.edu