Extended Lyα emission from a damped Lyα absorber at z = 3.115

Abstract

We searched for star formation activity associated with high-z damped Lyα systems (DLAs) with the Subaru telescope. We used a set of narrow-band (NB) filters whose central wavelengths correspond to the redshifted Lyα emission lines of targeted DLA absorbers at 3 < z < 4.5. We detected one apparent NB-excess object located 3.80 arcsec ( kpc) away from the quasar SDSS J031036.84+005521.7. Follow-up spectroscopy revealed an asymmetric Lyα emission at z em = 3.115 ± 0.003, which perfectly matches the sub-DLA trough at z abs = 3.1150 with logN(H I)/cm-2 = 20.05. The Lyα luminosity is estimated to be L Lyα = 1.07 × 1042 erg s-1, which corresponds to a star formation rate of 0.97 M yr-1. Interestingly, the detected Lyα emission is spatially extended with a sharp peak. The large extent of the Lyα emission is remarkably one-sided toward the quasar line-of-sight and is redshifted. The observed spatially asymmetric surface brightness profile can be qualitatively explained by a model of a DLA host galaxy, assuming a galactic outflow and a clumpy distribution of H I clouds in the circumgalactic medium. This large Lyα extension, which is similar to those found in Rauch et al., could be the result of complicated anisotropic radiative transfer through the surrounding neutral gas embedded in the DLA. © 2014. The American Astronomical Society. All rights reserved.