Connecting Lost Baryons and Dark Galaxies via QSO Absorption Lines

Abstract

Abstract. QSO absorption lines are sensitive to very low density gas, and consequently, QSO spectroscopy provides a powerful tool for measuring the distribution, physical conditions, and metal enrichment of baryons in the intergalactic medium and in "dark galaxies". However, ultraviolet spectroscopy is required to study QSO absorbers in the nearby universe where the connections between the absorbing gas and galaxies/environment can be probed. This talk reviewed several recent studies of low−z QSO absorbers in order to demonstrate the value of combining high-resolution ultraviolet spectroscopy with complementary information on the absorber environment, e.g., mapping of 21 cm emission in the vicinity of the absorbers; some notes on these examples are presented in this paper. The absorbers probed range from high−N (H I) damped Lyman α absorbers down to very low-column Lyα forest clouds with log N (H I) < 13.5. The high−N (H I) systems are candidate "dark galaxies" -these systems are more metal enriched than the high−z IGM, possibly due to in-situ star formation, and some of the absorbers are highly metal enriched. However, we have obtained follow-up 21cm emission mapping with the VLA and deep optical imaging, and while we do find H I clouds associated with the absorbers in 21cm emission, we often do not find any evidence of in-situ stars. At this juncture, it seems more likely that these low−z absorbers were enriched with metals within galaxies and were subsequently transported out into the IGM, e.g., by tidal stripping or galactic winds. This contribution also summarizes some recent results on the search for lost baryons in the "warm-hot" (shock-heated) low-redshift IGM.