Search for: All records

We report a Karl G. Jansky Very Large Array search for redshifted CO(1–0) emission from three Hi-absorption-selected galaxies atz≈ 2, identified earlier in their CO(3–2) or CO(4–3) emission. We detect CO(1–0) emission from DLA B1228-113 atz≈ 2.1933 and DLA J0918+1636 atz≈ 2.5848; these are the first detections of CO(1–0) emission in high-zHi-selected galaxies. We obtain high molecular gas masses,M_mol≈ 10¹¹× (α_CO/4.36)M_⊙, for the two objects with CO(1–0) detections, which are a factor of ≈1.5–2 lower than earlier estimates. We determine the excitation of the mid-JCO rotational levels relative to theJ= 1 level,r_J1, in Hi-selected galaxies for the first time, obtainingr₃₁= 1.00 ± 0.20 andr₄₁= 1.03 ± 0.23 for DLA J0918+1636, andr₃₁= 0.86 ± 0.21 for DLA B1228-113. These values are consistent with thermal excitation of theJ= 3 andJ= 4 levels. The excitation of theJ= 3 level in the Hi-selected galaxies is similar to that seen in massive main-sequence and submillimeter galaxies atz≳2, but higher than that in main-sequence galaxies atz≈ 1.5; the higher excitation of the galaxies atz≳ 2 is likely to be due to their higher star formation rate (SFR) surface density. We use Hubble Space Telescope Wide Field Camera 3 imaging to detect the rest-frame near-ultraviolet (NUV) emission of DLA B1228-113, obtaining an NUV SFR of 4.44 ± 0.47M_⊙yr⁻¹, significantly lower than that obtained from the total infrared luminosity, indicating significant dust extinction in thez≈ 2.1933 galaxy.

We report a NOrthern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter/submillimeter Array search for redshifted CO emission from the galaxies associated with seven high-metallicity ([M/H] ≥ −1.03) damped Lyαabsorbers (DLAs) atz≈ 1.64–2.51. Our observations yielded one new detection of CO(3–2) emission from a galaxy atz= 2.4604 using NOEMA, associated with thez= 2.4628 DLA toward QSO B0201+365. Including previous searches, our search results in detection rates of CO emission of$\approx {56}_{-24}^{+38}$% and$\approx {11}_{-9}^{+26}$%, respectively, in the fields of DLAs with [M/H] > −0.3 and [M/H] < −0.3. Further, the Hi–selected galaxies associated with five DLAs with [M/H] > −0.3 all have high molecular gas masses, ≳5 × 10¹⁰M_⊙. This indicates that the highest-metallicity DLAs atz≈ 2 are associated with the most massive galaxies. The newly identifiedz≈ 2.4604 Hi–selected galaxy, DLA0201+365g, has an impact parameter of ≈7 kpc to the QSO sightline, and an implied molecular gas mass of (5.04 ± 0.78) × 10¹⁰× (α_CO/4.36) × (r₃₁/0.55)M_⊙. Archival Hubble Space Telescope Wide Field and Planetary Camera 2 imaging covering the rest-frame near-ultraviolet (NUV) and far-ultraviolet (FUV) emission from this galaxy yield nondetections of rest-frame NUV and FUV emission, and a 5σupper limit of 2.3M_⊙yr⁻¹on the unobscured star formation rate (SFR). The low NUV-based SFR estimate, despite the very high molecular gas mass, indicates that DLA0201+365g either is a very dusty galaxy, or has a molecular gas depletion time that is around 2 orders of magnitude larger than that of star-forming galaxies at similar redshifts.