Galactic nebular lines in the fiber spectra of background QSOs: Reaching a hundred QSO-galaxy pairs with spectroscopic and photometric measurements

TL;DR

This study analyzes 103 QSO-galaxy pairs from SDSS, revealing properties of foreground galaxies through nebular emission lines, star formation rates, and absorption features, enhancing understanding of galaxy characteristics and their absorption systems.

Contribution

First comprehensive analysis of a large sample of QSO-galaxy pairs with spectroscopic and photometric data, providing insights into galaxy properties and absorption features.

Findings

Foreground galaxies are mostly late-type, star-forming.

Super-solar metallicities are common in the sample.

Anti-correlation between impact parameter and E(B-V)_(g-i).

Abstract

We present photometric and spectroscopic measurements of 53 QSO-galaxy pairs from the Sloan Digital Sky Survey, where nebular emission lines from a 0<z<0.84 foreground galaxy are detected in the fiber spectra of a background QSO, bringing the overall sample to 103 QSO-galaxy pairs detected in the SDSS. We here study the nature of these systems. Detected foreground galaxies appear at impact parameters between 0.37 kpc and 12.68 kpc. The presence of oxygen and Balmer emission lines allows us to determine the emission line metallicities for our sample, which are on average super-solar in value. Star formation rates for our sample are in the range 0.01-12 M_sol yr^-1. We utilize photometric redshift fitting techniques to estimate the M_stellar values of our galaxies (log M_stellar = 7.34 - 11.54), and extrapolate this relationship to those galaxies with no imaging detections. Where available, we measure the absorption features present in the QSO spectrum due to the foreground galaxy and the relationships between their rest equivalent widths. We report an anti-correlation between impact parameter and E(B-V)_(g-i), as well as a correlation between galaxy color (u-r) and E(B-V)_(g-i). We find that our sample is one of late-type, star forming galaxies comparable to field galaxies in a similar redshift range, providing important clues to better understand absorption systems. These galaxies represent a sample of typical galaxies in the local Universe for which abundances, extinction, morphology, and absorption properties may be measured using background QSOs with great potential for follow-up observations.