Identifying MgII Absorption Systems in Strong Gravitational Lens Quasars from the SDSS Quasar Lens Search (SQLS) Data

Based on the SDSS Quasar Lens Search (SQLS) data, we selected 13 strong gravitational lens quasar sources with two images. Using the latest DR18 spectroscopic data from SDSS, we searched for MgII' λλ2796, 2803 absorption systems in the observed wavelength range of 3800-6000Å. By normalizing and fitting the absorption lines in the spectra of the two images separately, we identified a total of 19 MgII absorption systems, with absorption redshifts ranging from [range]. Assuming that the MgII absorbers correspond to deflectors of the quasar light, we found that 69% (9/13) of the lens galaxy redshifts were consistent with previous estimates by other researchers. For cases with multiple absorption systems, assuming that the absorbers collectively contribute to the lensing effect, we estimated the range of equivalent lens redshifts. We found that the lens redshift values estimated by other researchers were all within the range of equivalent lens redshifts. Therefore, we believe that the identification of MgII absorption systems is of significant importance for the search for strong gravitational lens quasar candidate systems and the estimation of lens galaxy redshifts.