Quasars as a tracer of large-scale structures in the distant universe

TL;DR

This study investigates how quasar number density and properties correlate with large-scale galaxy density at redshifts 0.46 to 0.59, revealing a power-law relation and weak property dependencies, suggesting quasars as tracers of cosmic structures.

Contribution

It provides the first large-scale analysis of quasar-galaxy density correlations at intermediate redshifts using SDSS data, highlighting potential for high-redshift structure studies.

Findings

Quasar number density correlates with galaxy density as a power law.

Weak positive correlation between black hole mass and density.

Weak negative correlation between quasar luminosity and density.

Abstract

We study the dependence of the number density and properties of quasars on the background galaxy density using the currently largest spectroscopic datasets of quasars and galaxies. We construct a galaxy number density field smoothed over the variable smoothing scale of between approximately 10 and $20\,h^{-1}$Mpc over the redshift range of $0.46<z<0.59$ using the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12) Constant MASS (CMASS) galaxies. The quasar sample is prepared from the SDSS I/II DR7. We examine the correlation of incidence of quasars with the large-scale background density and dependence of quasar properties such as bolometric luminosity, black hole mass, and Eddington ratio on the large-scale density. We find a monotonic correlation between the quasar number density and large-scale galaxy number density, which is fitted well with a power law relation, $n_Q\propto\rho_G^{0.618}$. We detect weak dependences of quasar properties on the large-scale density such as a positive correlation between black hole mass and density, and a negative correlation between luminosity and density. We discuss the possibility of using quasars as a tracer of large-scale structures at high redshifts, which may be useful for studies of growth of structures in the high redshift universe.