Quasars as tracers of cosmic flows

TL;DR

This paper explores using quasars as tools to measure the universe's expansion history, leveraging their luminosity and emission line properties across a wide redshift range, with initial promising results from spectroscopic observations.

Contribution

It introduces a novel method to utilize quasars as standard candles for cosmology, based on emission line and luminosity relations, extending measurements to higher redshifts than supernovae.

Findings

Spectroscopic observations of a quasar at z=0.9 show promising variability patterns.

The method demonstrates potential for measuring cosmic expansion using quasars.

Initial results support the feasibility of quasar-based cosmological measurements.

Abstract

Quasars, as the most luminous persistent sources in the Universe, have broad applications for cosmological studies. In particular, they can be employed to directly measure the expansion history of the Universe, similarly to SNe Ia. The advantage of quasars is that they are numerous, cover a broad range of redshifts, up to $z = 7$, and do not show significant evolution of metallicity with redshift. The idea is based on the relation between the time delay of an emission line and the continuum, and the absolute monochromatic luminosity of a quasar. For intermediate redshift quasars, the suitable line is Mg II. Between December 2012 and March 2014, we performed five spectroscopic observations of the QSO CTS C30.10 ($z = 0.900$) using the South African Large Telesope (SALT), supplemented with photometric monitoring, with the aim of determining the variability of the line shape, changes in the total line intensity and in the continuum. We show that the method is very promising.