Galaxy counterparts of metal-rich damped Lyα absorbers - I. The case of the z= 2.35 DLA towards Q 2222−0946 Galaxy counterparts of metal-rich damped Lyα absorbers - I. The case of the z= 2.35 DLA towards Q 2222−0946 J. P. U. Fynbo et al. Galaxy counterparts of metal-rich DLAs

We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyα absorbers (DLAs). Our rationale is that high-metallicity DLAs due to the luminosity-metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Lyα emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([O ], [O ], Hβ and Hα) fall in the near-infrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the DLA towards the quasar Q 0946. This DLA is amongst the most metal-rich DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn , Si , Ni , Mn and Fe of and , respectively. The galaxy is detected in the Lyα, [O ]λλ4959, 5007 and Hα emission lines at an impact parameter of about 0.8 arcsec (6 kpc at ). Based on the Hα line, we infer a star formation rate of 10 M yr, which is a lower limit due to the possibility of slit loss. Compared to the recently determined Hα luminosity function for galaxies, the DLA-galaxy counterpart has a luminosity of . The emission-line ratios are 4.0 (Lyα/Hα) and 1.2 ([O ]/Hα). In particular, the Lyα line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA are consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts. [ABSTRACT FROM AUTHOR]