Paper detail

Discovery of a damped Ly$α$ galaxy at z $\sim$ 3 towards the quasar SDSS J011852+040644

We report the detection of the host galaxy of a damped Ly$α$ system (DLA) with log N(HI) $ [\rm cm^{-2}]$ = $21.0 \pm 0.10$ at $z \approx 3.0091$ towards the background quasar SDSS J011852+040644 using the Palomar Cosmic Web Imager (PCWI) at the Hale (P200) telescope. We detect Ly$α$ emission in the dark core of the DLA trough at a 3.3$σ$ confidence level, with Ly$α$ luminosity of $L_{\rm Lyα}$ $\rm = (3.8 \pm 0.8) \times 10^{42}\ erg\ s^{-1}$, corresponding to a star formation rate of $\gtrsim 2\ \rm M_{\odot}\ yr^{-1}$ (considering a lower limit on Ly$α$ escape fraction $f_{esc}^{Lyα} \sim 2\%$) as typical for Lyman break galaxies at these redshifts. The Ly$α$ emission is blueshifted with respect to the systemic redshift derived from metal absorption lines by $281 \pm 43$ km/s. The associated galaxy is at very small impact parameter of $\lesssim 12 \rm\ kpc$ from the background quasar, which is in line with the observed anticorrelation between column density and impact parameter in spectroscopic searches tracing the large-scale environments of DLA host galaxies.