A [C <scp>ii</scp>] 158 <i>μ</i>m Survey of Damped Lyα Absorber Galaxies at <i>z</i> ∼ 4: Observations of Dense and Metal-enriched Neutral Gas within the Circumgalactic Medium of Star-forming Galaxies

Abstract We present a survey undertaken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the galaxies associated with a representative sample of 16 damped Ly α absorbers (DLAs) at z ≈ 4.1–4.5, using the [C ii ] 158 μ m ([C ii ]) line. We detect seven [C ii ]-emitting galaxies in the fields of five DLAs, all of which have absorption metallicity [M/H] &gt; −1.5. We find that the detectability of these H i -selected galaxies with ALMA is a strong function of DLA metallicity, with a detection rate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>7</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>20</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> % for DLAs with [M/H] &gt; −1.5 and 0 +18 % for DLAs with [M/H] &lt; −1.5. The identified DLA galaxies have far-IR properties similar to those of typical star-forming galaxies at z ∼ 4, with estimated obscured star formation rates ranging from ≲6 M ⊙ yr −1 to 110 M ⊙ yr −1 . High-metallicity DLAs therefore provide an efficient way to identify and study samples of high-redshift, star-forming galaxies, without preselecting the galaxies by their emission properties. The agreement between the velocities of the metal absorption lines of the DLA and the [C ii ] emission line of the DLA galaxy indicates that the metals within the DLA originated in the galaxy. With observed impact parameters between 14 and 59 kpc, this indicates that star-forming galaxies at z ∼ 4 have a substantial reservoir of dense, cold, neutral gas within their circumgalactic medium that has been enriched with metals from the galaxy.