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

TL;DR

This study investigates the properties of companion galaxies near low redshift quasars, revealing that many show signs of recent star formation likely triggered by interactions, but the quasars' influence on star formation appears limited.

Contribution

First detailed spectroscopic analysis of close companion galaxies to low redshift quasars in SDSS Stripe 82, linking galaxy interactions to star formation activity.

Findings

Most companion galaxies are physically associated with quasars.

Many companions show emission lines indicating recent star formation.

Quasars have limited impact on inducing star formation in nearby galaxies.

Abstract

We obtained optical spectroscopy of close (< 80 kpc) companion objects of a sample of 12 low redshift quasars (z < 0.3 ) selected from the SDSS Stripe82 area and that are in the subsample of 52 QSOs for which both multicolor host galaxies properties and galaxy environment was recently investigated in detail. We found that for 8 out of 12 sources the companion galaxy is associated to the QSO having a difference of radial velocity that is less than 400 km/s. Many of these associated companions exhibit [OII] $\lambda$3727 \AA~ emission lines suggestive of episodes of (recent) star formation possibly induced by past interactions. The SFR of the companion galaxies as derived from [OII] line luminosity is, however, modest, with a median value of 1.0 +-0.8 M_sun/yr, and the emission lines are barely consistent with expectation from gas ionization by the QSO. The role of the QSO for inducing star formation in close companion galaxies appears meager. For three objects we also detect the starlight spectrum of the QSO host galaxy which is characterized by absorption lines of old stellar population and [OII] emission line.