Discovery of a Low-redshift Damped Lyα System in a Foreground Extended Disk Using a Starburst Galaxy Background Illuminator

Christopher M. Dupuis, Sanchayeeta Borthakur, Mansi Padave, Rolf A. Jansen, Rachael M. Alexandroff, Timothy M. Heckman

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


We present the discovery of a low-redshift damped Lyα (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 (z = 0.17514). The DLA is at an impact parameter of ρ = 36 kpc from the star-forming galaxy, SDSS J111324.08+293051.2 (z = 0.17077). We measure an H i column density of N(H i) = 3.47 1020 cm-2 along with multiple low-ionization species such as N i, N ii, Si ii, C ii, and Si iii. We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be A DLA ≥ 3.3 kpc2. Assuming a uniform column density over the entire DLA system, we estimate its mass to be M DLA ≥ 5.3 106 M o˙. The extended illuminator and the low redshift of this DLA give us the unique opportunity to characterize its nature and the connection to its host galaxy. We measure a velocity offset of +131 km s-1 from the systemic velocity of the host for the DLA. This velocity is -84 km s-1 from the projected rotation velocity of the host galaxy as measured using a newly constructed rotation curve. Based on the size of the host galaxy, the H i column density, and the gas kinematics, we believe this DLA is tracing the warm neutral gas in the H i disk of the foreground galaxy. Our detection adds to a small set of low-redshift DLAs that have confirmed host galaxies, and is the first to be found using an extended background source.

Original languageEnglish (US)
Article number103
JournalAstrophysical Journal
Issue number2
StatePublished - Feb 1 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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