Constraining MgII absorbers with the SDSS
  Using a large sample of MgII absorbers with 0.4<z<2.2 detected by Nestor et al (2005) in the Early Data Release of the SDSS, we present new constraints on the physical properties of these systems based on two statistical analyses: (i) By computing the ratio between the composite spectra of quasars with and without absorbers, we measure the reddening effects induced by these intervening systems; and (ii) by stacking SDSS images centered on quasars with strong MgII absorption lines and isolating the excess light around the PSF, we measure the mean luminosity and colors of the absorbing galaxies. This statistical approach does not require any spectroscopic follow up and allows us to constrain the photometric properties of absorber systems. 
Brice M\'enard (1), Stefano Zibetti (2), Daniel Nestor (3) and David   Turnshek (4) ((1) Institute for Advanced Study, (2) M...