[O II] nebular emission from MgII absorbers: star formation associated with the absorbing gas

We present nebular emission associated with 198 strong MgII absorbers at 0.35 <= z <= 1.1 in the fibre spectra of quasars from the Sloan Digital Sky Survey. Measured [O II] luminosities (L-[O II]) are typical of sub-L* galaxies with derived star formation rate (uncorrected for fibre losses and dust reddening) in the range of 0.5-20 M-circle dot yr(-1). Typically less than similar to 3 per cent of the Mg II systems with rest equivalent width, W-2796 >= 2 angstrom, show L*([O II]) >= 0.3L([O II]). The detection rate is found to increase with increasing W-2796 and z. No significant correlation is found between W-2796 and L-[O II] even when we restrict the samples to narrow z ranges. A strong correlation is seen between L-[O II] and z. While this is expected from the luminosity evolution of galaxies, we show that finite fibre size plays a very crucial role in this correlation. The measured nebular line ratios (like [OIII]/[O II] and [O III]/H beta) and their z evolution are consistent with those of galaxies detected in deep surveys. Based on the median stacked spectra, we infer the average metallicity (log Z similar to 8.3), ionization parameter (log q similar to 7.5) and stellar mass (log (M/M-circle dot) similar to 9.3). The MgII systems with nebular emission typically have W-2796 >= 2 angstrom, MgII doublet ratio close to 1 andW(Fe II lambda 2600)/W-2796 similar to 0.5 as often seen in damped Ly a and 21-cm absorbers at these redshifts. This is the biggest reported sample of [OII] emission from MgII absorbers at low-impact parameters ideally suited for probing various feedback processes at play in z <= 1 galaxies.