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T. M. Tripp, E. B. Jenkins (Princeton University), G. M. Williger (JHU), S. R. Heap (NASA-Goddard), STIS ID Team
Using high signal-to-noise echelle spectra obtained with the Space Telescope Imaging Spectrograph with 7 km/s resolution (FWHM), we report detections of C II, Si II, and Si III absorption lines in the Ly\alpha absorber at z(abs) = 0.00530 in the spectrum of 3C 273. This Ly\alpha absorber is notable because (1) it is situated within the southern extension of the Virgo cluster, and (2) observations with the Far Ultraviolet Spectroscopic Explorer have revealed Ly\beta - Ly\theta absorption lines at the same redshift, thereby accurately constraining the H I column density. We model the ionization of the gas and derive [C/H] = -1.2+0.3-0.2, [Si/C] = +0.2±0.1, and log nH= -2.8±0.3. Although there is a limited number of Milky Way sight lines in which carbon and silicon abundances have been reliably measured in the same interstellar cloud, we argue based on comparison to the Milky Way ISM that the overabundance of Si relative to C is unlikely to be due to depletion onto dust grains. Instead, this probably indicates that the gas has been predominately enriched by ejecta from type II supernovae. This enrichment is most plausibly provided by an unbound galactic wind, given the absence of known galaxies within a projected distance of ~100 kpc and the presence of galaxies capable of driving a wind at larger distances (e.g., H I 1225+01). Such processes have been invoked to explain the observed abundances in the hot, X-ray emitting gas in Virgo. However, the sight line to 3C 273 is more than 10 degrees away from the region of X-ray emission, and this indicates that such winds are widespread in the Virgo cluster, and may be common outside of the cluster environment.