Molecular Emission from a Galaxy Associated with a z~2.2 Damped Lyman-alpha Absorber

TL;DR

This study reports the detection of molecular and dust emission from a galaxy at z~2.2 associated with a high-metallicity DLA, revealing complex multi-phase gas and supporting the link between high-metallicity DLAs and massive galaxies.

Contribution

First detection of CO(3-2) and far-infrared emission from a high-metallicity DLA galaxy at z~2.2, linking molecular gas, dust, and metal content to galaxy mass and environment.

Findings

Galaxy has high molecular mass (~10^11 Msun) and star formation rate (~110 Msun/yr).

DLA gas shows both warm HI and cold components with significant metal content.

Redshift alignment suggests minimal bulk motion of gas relative to galaxy.

Abstract

Using the Atacama Large Millimeter/sub-millimeter Array, we have detected CO(3-2) line and far-infrared continuum emission from a galaxy associated with a high-metallicity ([M/H] = -0.27) damped Ly-alpha absorber (DLA) at z =2.19289. The galaxy is located 3.5" away from the quasar sightline, corresponding to a large impact parameter of 30 kpc at the DLA redshift. We use archival Very Large Telescope-SINFONI data to detect Halpha emission from the associated galaxy, and find that the object is dusty, with a dust-corrected star formation rate of 110 +60 -30 Msun/yr. The galaxy's molecular mass is large, Mmol = (1.4 +- 0.2) x 10^11 x (\alpha_CO/4.3) x (0.57/r_31) Msun, supporting the hypothesis that high-metallicity DLAs arise predominantly near massive galaxies. The excellent agreement in redshift between the CO(3-2) line emission and low-ion metal absorption (~40 km/s) disfavors scenarios whereby the gas probed by the DLA shows bulk motion around the galaxy. We use Giant Metrewave Radio Telescope HI 21cm absorption spectroscopy to find that the HI along the DLA sightline must be warm, with a stringent lower limit on the spin temperature of T_s > 1895 x (f/0.93) K. The detection of CI absorption in the DLA, however, also indicates the presence of cold neutral gas. To reconcile these results requires that the cold components in the DLA contribute little to the HI column density, yet contain roughly 50% of the metals of the absorber, underlining the complex multi-phase nature of the gas surrounding high-z galaxies.