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A. Athey, J. Bregman (U. of Michigan)
In the study of the hot interstellar medium in elliptical galaxies, one of the most contentious issues is the metallicity of the gas. The metallicity is an important parameter in the ISM because it provides insight to the origin of the gas, its mass and eventual evolution. Currently, the metallicity measurements are being determined from X-ray telescopes, such as Chandra and XMM. We conducted a program to obtain an independent determination of this critical quantity with ground based optical spectra from the 2.4m Hilter Telescope at MDM. Trinchieri & Alighieri (1991) investigated a sample of X-ray emitting galaxies through narrow-band optical imaging and found a large fraction (<85%) of X-ray bright galaxies to have optical emission lines (H-alpha and [N II]). Because the structure of this emission line gas is similar to the X-ray emission, it is likely tracing the cooling of the X-ray gas or possibly the injection of mass into the ISM from dying stars. We present optical spectra of 14 elliptical galaxies with wavelength coverage from 3200 Å- 5100 Åand 5600 Å- 7150 Å (NGC720, NGC1407, NGC1600, NGC2768, NGC3377, NGC3379, NGC3607, NGC4125, NGC4472, NGC4494, NGC4552, NGC4636, NGC5846). This wavelength coverage allows us to detect major lines for metallicity determinations, including [O I] 6300 Å, [O II] 3727 Å, [O III] 4363, 5007 Å, [N II] 6583Å, [S II] 6725 Å, as well as H-alpha and H-beta. In 6 of these 14 galaxies we detect emission line gas. In 4 of these galaxies we have complete information to determine metallicites.
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