Molecular Emission from a Galaxy Associated with a z ∼ 2.2 Damped Ly α Absorber

Abstract

Using the Atacama Large Millimeter/submillimeter 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 Lyα absorber (DLA) at z_DLA = 2.19289. The galaxy is located 3farcs5 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 Hα emission from the associated galaxy, and find that the object is dusty, with a dust-corrected star formation rate of 110_-30⁺⁶⁰ M_⊙ yr^-1. The galaxy's molecular mass is large, Mmol = (1.4 ± 0.2) × 1011 × (αCO/4.3) × (0.57/r31) M_⊙, 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^-1) disfavors scenarios whereby the gas probed by the DLA shows bulk motion around the galaxy. We use Giant Metrewave Radio Telescope H i 21 cm absorption spectroscopy to find that the H i along the DLA sightline must be warm, with a stringent lower limit on the spin temperature of Ts < 1895 × (f/0.93) K. The detection of C i 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 H i 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. 110_-30⁺⁶⁰