Low-redshift quasars in the SDSS Stripe 82 II: associated companion galaxies and signature of star formation

TL;DR

This study investigates the properties of companion galaxies around low-redshift quasars, revealing that many exhibit recent star formation, but quasars do not significantly affect their companions' star formation activity.

Contribution

It provides new spectroscopic data on companion galaxies of low-redshift quasars, expanding the sample size and analyzing star formation signatures in these galaxies.

Findings

44% of quasars have associated companion galaxies.

67% of these companions show signs of recent star formation.

Host galaxies include post-starburst types.

Abstract

We present optical spectroscopy of the close companions of 22 low redshift (z<0.5) quasars (QSO) selected from a larger sample of QSO in the SDSS Stripe82 region for which both the host galaxy and the large scale environments have been investigated in our previous work. The new observations extend the number of QSO studied in our previous paper on close companion galaxies of 12 quasars. Our analysis here covers all 34 quasars from both this work and the previously published paper. We find that half of them (15 QSO; $\sim$44%) have at least one associated galaxy. Many (12 galaxies; $\sim$67%) of the associated companions exhibit [OII] 3727 A emission line as signature of recent star formation. The star formation rate (SFR) of these galaxies is modest (median SFR $\sim$ 4.3 M$_{\odot}$ yr$^{-1}$). For 8 QSO we are also able to detect the starlight of the host galaxy from which 3 have a typical spectrum of a post-starburst galaxy. Our results suggest that quasars do not have a strong influence on the star formation of their companion galaxies.