The Cosmic Ultraviolet Baryon Survey (CUBS). II. Discovery of an H 2 -bearing DLA in the Vicinity of an Early-type Galaxy at z = 0.576*

• Main Authors: Boettcher, Erin (Author), Chen, Hsiao-Wen (Author), Zahedy, Fakhri S (Author), Cooper, Thomas J (Author), Johnson, Sean D (Author), Rudie, Gwen C (Author), Chen, Mandy C (Author), Petitjean, Patrick (Author), Cantalupo, Sebastiano (Author), Cooksey, Kathy L (Author), Faucher-Giguère (Author), Greene, Jenny E (Author), Lopez, Sebastian (Author), Mulchaey, John S (Author), Penton, Steven V (Author), Putman, Mary E (Author), Rafelski, Marc (Author), Rauch, Michael (Author), Schaye, Joop (Author), Simcoe, Robert A (Author), Walth, Gregory L (Author)
• Format: Article
• Language: English
• Published: American Astronomical Society, 2022-04-29T16:38:41Z.
• Subjects: Article
• Online Access: Get fulltext

 We report the serendipitous detection of an H2-bearing damped Lyα 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(H2)/cm−2] $={18.97}_{-0.06}^{+0.05}$. The diffuse molecular gas is found in two velocity components separated by Δ ν ≈ 60 km s−1, with >99.9% of the total H2 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 κO ≈ 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 νg ≤ 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 H2 absorber. The close proximity of the H2-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.