Newly Recognized QSO/Galaxy Pairs at Small Impact Parameters for Low Redshift Galaxies

Abstract

A search for emission lines in foreground galaxies, in QSO spectra (zgal << zQSO) of the SDSS data release 5, reveals 21 examples of QSOs shining through low redshift, foreground galaxies at low impact parameters (<10 kpc). About 74,000 QSO spectra were examined, by searching for narrow H emission lines at z < 0.295, at a flux level greater than 5 x 10-17 ergs/cm2·sec, then confirming that other expected emission lines of the H II regions in the galaxy are detected. The measurements show that the galaxies have abundances of solar or above and star formation rates between 10 and 1000 solar masses per year. The galaxies were deblended from the QSOs to get colors and shapes. For cases that allow the galaxy and the QSO to be deblended, the galaxies are blue [1.0 < (u-r) < 1.9]. Extinction through the galaxies is determined from the color excesses of the QSOs. The color excesses range from 0 to 0.25 magnitudes. These extinction values are compared with the flux ratios of H and H, which reflect the extinction for an undetermined fraction of the sightline through each galaxy. Measurement or limits on galactic, interstellar Ca II and Na I absorption are given, from the QSO spectrum. The technique used is compared with other ways of finding QSO/galaxy pairs, for the purpose of designing an experiment to characterize the absorption properties of gas in galaxies at distances from the galaxy centers < 10 kpc.