Environment of SDSS quasars at $z=0.4$$-$$1.0$ explored by Subaru HSC

TL;DR

This study explores the environments of SDSS quasars at redshifts 0.4 to 1.0 using Subaru HSC data, finding that quasars tend to reside in slightly less dense galaxy environments than similar galaxies, with no correlation to black hole properties.

Contribution

It provides a large-scale, deep analysis of quasar environments at intermediate redshifts, revealing that quasar activity is not directly linked to local galaxy density.

Findings

Galaxy density around quasars is 11-20% lower than matched galaxies.

No correlation between galaxy density and quasar black hole mass.

Quasar activity likely not triggered by local galaxy density.

Abstract

The relationship between quasars and their galaxy environment is important for understanding the evolution of galaxies and supermassive black holes, but it is not fully understood. We perform a wide and deep exploration of the environment of quasars at $0.4 < z < 1.0$ using the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey. We investigate the environment of the 1,912 spectroscopically selected quasars from the Sloan Digital Sky Survey (SDSS), using photometrically selected galaxies from the HSC-SSP data, over an area of 505 deg${^{2}}$. The quasar environment is compared to the environment of matched galaxies with similar stellar mass and redshift. We employ the $k$-nearest neighbor method to define the local galaxy number density for both the quasars and the matched galaxies at a scale of a few hundred kpc. As a result, we find that the number density of galaxies around SDSS quasars is lower than that of the matched galaxies by $\sim$11--$20\%$. We also investigate possible correlations between the local galaxy number densities and the quasar properties such as black hole mass and Eddington ratio. As a result, no correlation is found between the local galaxy number densities and these properties of quasars. These results suggest that the quasar activity is not triggered by the high number density of surrounding galaxies at the scale of a few hundred kpc.