Discovery of a Dwarf Poststarburst Galaxy near a High Column Density Local Lyα Absorber

We report the discovery of a dwarf (M_B = -13.9) post-starburst galaxycoincident in recession velocity (within uncertainties) with the highest columndensity absorber (N_HI = 10^15.85 cm^{-2} at cz = 1586 km/s) in the 3C~273sightline. This galaxy is by far the closest galaxy to this absorber, projectedjust 71 kpc on the sky from the sightline. The mean properties of the stellarpopulations in this galaxy are consistent with a massive starburst ~3.5 Gyrsago, whose attendant supernovae, we argue, could have driven sufficient gasfrom this galaxy to explain the nearby absorber. Beyond the proximity on thesky and in recession velocity, the further evidence in favor of this conclusionincludes both a match in the metallicities of absorber and galaxy, and the factthat the absorber has an overabundance of Si/C, suggesting recent type IIsupernova enrichment. Thus, this galaxy and its ejecta are the expectedintermediate stage in the fading dwarf evolutionary sequence envisioned byBabul & Rees to explain the abundance of faint blue galaxies at intermediateredshifts.Comment: 33 pages, 4 figures, ApJ in pres