AAS 201st Meeting, January, 2003
Session 26. Galaxy Structure and Interactions
Oral, Monday, January 6, 2003, 10:00-11:30am, 616-617

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[26.03D] On the Origin of the Interstellar Medium in Elliptical Galaxies

A. E. Athey, J. N. Bregman (University of Michigan)

The data from the recently launched Chandra and XMM-Newton Observatories have shown with impressive clarity the structure of the hot (T~106-7K) gas and finally resolved out the point-source emission. However, the exact origin of the interstellar medium (ISM) remains in question. The majority of the gas is presumed to come from the stellar mass loss of old, near-solar metallicity stars with some additional contribution from in-falling group or cluster medium. However, the majority of the studies with previous X-ray satellites have concluded a substantially sub-solar metallicity. We used the Infrared Space Observatory (ISO) to observe stellar mass loss from AGB stars in narrow band mid-IR imaging. Galaxy-wide mass loss rates were determined via the calibration of a dust vibrational-mode emission line with equivalent emission from Galactic and LMC AGB stars. This rate combined with studies of supernovae (SN) rates and stellar metallicities provides a current estimate of mass injection rates and general ISM enrichment in early-type galaxies. Approximately half of elliptical galaxies exhibit optical line emission from warm (T~3000K) gas, revealed through narrow band H-alpha imaging. We obtained optical spectroscopy on twenty elliptical galaxies to determine the metallicity of this intermediate temperature gas. Either this gas is being thermalized from the AGB mass loss or it is gas that has cooled out of the hot phase. In either case, it provides a link to the hot phase and an independent constraint on metallicities determined in the X-rays. Finally, we analyzed all of the early-type galaxy data in the Chandra archive and find that a single value for the metallicity of the dominant X-ray lines (iron, magnesium, silicon, sulfur, neon and oxygen) is inconsistent with the data. Nearly universally, silicon, magnesium, sulfur and neon are over-abundant relative to iron while oxygen is equally or under-abundant to iron. These ratios are expected for a gas with an enrichment history dominated by SN type Ia. An up to date physical picture is presented for the origin of the ISM in early-type galaxies, reconciling the data from the gas and stars with some environmental influences being revealed.

The author(s) of this abstract have provided an email address for comments about the abstract: aathey@umich.edu

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