Journal ArticleA Massive H <scp>i</scp> -absorption-selected Galaxy at <i>z</i>  ≈ 2.356Kaur, B; Kanekar, N; Neeleman, M; Zhu, Y; Prochaska, J X; Rafelski, M; Becker, G<title>Abstract</title> <p>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<sc>i</sc>-selected galaxy, DLA1020+2733g, at<italic>z</italic> ≈ 2.3568 in the field of the<italic>z</italic>= 2.3553 damped Ly<italic>α</italic>absorber (DLA) toward QSO J1020+2733. The VLA CO(1–0) detection yields a molecular gas mass of (2.84 ± 0.42) × 10¹¹ × (<italic>α</italic>_CO/4.36)<italic>M</italic>_⊙, the largest ever measured in an H<sc>i</sc>-selected galaxy. The DLA metallicity is +0.28 ± 0.16, from the Zn<sc>ii</sc><italic>λ</italic>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<italic>M</italic>_⊙yr⁻¹from the rest-frame 349 GHz continuum emission and a relatively long molecular gas depletion timescale of ≳0.6 Gyr. The excitation of the<italic>J</italic>= 3 rotational level is subthermal, with<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><msub><mrow><mi>r</mi></mrow><mrow><mn>31</mn></mrow></msub><mo>≡</mo><mrow><mi>L</mi></mrow><msub><mrow><mi>′</mi></mrow><mrow><mi mathvariant='normal'>CO</mi><mo stretchy='false'>(</mo><mn>3</mn><mo>−</mo><mn>2</mn><mo stretchy='false'>)</mo></mrow></msub><mo>/</mo><mrow><mi>L</mi></mrow><msub><mrow><mi>′</mi></mrow><mrow><mi mathvariant='normal'>CO</mi><mo stretchy='false'>(</mo><mn>1</mn><mo>−</mo><mn>0</mn><mo stretchy='false'>)</mo></mrow></msub><mo>=</mo><mn>0.513</mn><mo>±</mo><mn>0.081</mn></math></inline-formula>, 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.</p>The Astrophysical Journal2025-03-1910627312The Astrophysical Journal Letters9821L262041-8205https://doi.org/10.3847/2041-8213/adb83d2107989; 2107991; 2534994National Science Foundation