A Massive H <scp>i</scp>-absorption-selected Galaxy at <i>z</i> ≈ 2.356

Abstract We use the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array to detect CO(1–0), CO(3–2), and rest-frame 349 GHz continuum emission from an H i -selected galaxy, DLA1020+2733g, at z ≈ 2.3568 in the field of the z = 2.3553 damped Ly α absorber (DLA) toward QSO J1020+2733. The VLA CO(1–0) detection yields a molecular gas mass of (2.84 ± 0.42) × 10 11 × ( α CO /4.36) M ⊙ , the largest ever measured in an H i -selected galaxy. The DLA metallicity is +0.28 ± 0.16, from the Zn ii λ 2026 absorption line detected in a Keck Echellette Spectrograph and Imager spectrum. This continues the trend of high-metallicity DLAs being frequently associated with massive galaxies. We obtain a star formation rate (SFR) of ≲400 M ⊙ yr −1 from the rest-frame 349 GHz continuum emission and a relatively long molecular gas depletion timescale of ≳0.6 Gyr. The excitation of the J = 3 rotational level is subthermal, with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>31</mml:mn> </mml:mrow> </mml:msub> <mml:mo>≡</mml:mo> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>′</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">CO</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>′</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">CO</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.513</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.081</mml:mn> </mml:math> , suggesting that DLA1020+2733g has a low SFR surface density. The large velocity spread of the CO lines, ≈500 km s −1 , and the long molecular gas depletion timescale suggest that DLA1020+2733g is likely to be a cold rotating-disk galaxy.