The Cosmic Ultraviolet Baryon Survey (CUBS). II. Discovery of an H<sub>2</sub>-bearing DLA in the Vicinity of an Early-type Galaxy at z = 0.576*
Erin Boettcher, Hsiao‐Wen Chen, Fakhri S. Zahedy, Thomas J. Cooper, Sean D. Johnson, Gwen C. Rudie, Mandy C. Chen, Patrick Petitjean, Sebastiano Cantalupo, Kathy L. Cooksey, Claude‐André Faucher‐Giguère, Jenny E. Greene, Sebastián López, John S. Mulchaey, Steven V. Penton, M. E. Putman, Marc Rafelski, Michael Rauch, Joop Schaye, Robert A. Simcoe, Gregory Walth
Abstract
Abstract We report the serendipitous detection of an H 2 -bearing damped Ly α absorber at z = 0.576 in the spectrum of the QSO J0111–0316 in the Cosmic Ultraviolet Baryon Survey. Spectroscopic observations from Hubble Space Telescope-COS in the far-ultraviolet reveal a damped absorber with log[ N (H i )/cm −2 ] = 20.1 ± 0.2 and log[ N (H 2 )/cm −2 ] . The diffuse molecular gas is found in two velocity components separated by Δ ν ≈ 60 km s −1 , with >99.9% of the total H 2 column density concentrated in one component. At a metallicity of ≈50% of solar, there is evidence for Fe enhancement and dust depletion, with a dust-to-gas ratio κ O ≈ 0.4. A galaxy redshift survey conducted with IMACS and LDSS-3C on Magellan reveals an overdensity of nine galaxies at projected distance d ≤ 600 proper kpc (pkpc) and line-of-sight velocity offset Δ ν g ≤ 300 km s −1 from the absorber. The closest is a massive, early-type galaxy at d = 41 pkpc that contains ≈70% of the total stellar mass identified at d ≤ 310 pkpc of the H 2 absorber. The close proximity of the H 2 -bearing gas to the quiescent galaxy and the Fe-enhanced chemical abundance pattern of the absorber suggest a physical connection, in contrast to a picture in which DLAs are primarily associated with gas-rich dwarfs. This case study illustrates that deep galaxy redshift surveys are needed to gain insight into the diverse environments that host dense and potentially star-forming gas.