In The Neighbourhood of Tame Monsters: A study of galaxies near low-redshift quasars

TL;DR

This study investigates the environments of low-redshift quasars, revealing a higher density of blue neighboring galaxies and suggesting a merging scenario for quasar formation, with no significant impact on galaxy properties.

Contribution

It provides the most comprehensive analysis to date of quasar environments at low redshift using SDSS data, focusing on galaxy densities and properties around quasars.

Findings

Increased surface density of blue neighbors near quasars

No significant change in star formation or galaxy properties with distance

Supports merging scenario for quasar formation

Abstract

The impact of quasars on their galaxy neighbours is an important factor in the understanding of galaxy evolution models. The aim of this work is to characterize the intermediate-scale environments of quasars at low redshift (z $<$ 0.2) with the most statistically complete sample to date using the seventh data release of the Sloan Digital Sky Survey. We have used 305 quasar-galaxy associations with spectroscopically measured redshifts within the projected distance range of 350 kpc, to calculate how surface densities of galaxies, colors, degree of ionization, dust extinction and star-formation rates change as a function of the distance to our quasar sample. We also identify the companion Active Galactic Nuclei from our main galaxy sample and calculate surface density for different galaxy types. We have done this in three different quasar-galaxy redshift difference ranges $|\Delta$z$|<$ 0.001, 0.006, and 0.012. Our results suggest that there is a significant increase of the surface density of blue neighbours around our low-redshift quasar sample that is steeper than around non-active field galaxies of the same luminosity and redshift range. This may indicate that quasar formation is accomplished via a merging scenario. No significant changes in star formation rate, dust extinction, degree of ionization or color as a function of distance from the quasars was observed. We could not observe any effects from quasars on their companion galaxies.