Quasar UV luminosity function evolution up to z=8

TL;DR

This paper analyzes the evolution of the quasar UV luminosity function up to redshift 8, combining observational data to predict quasar contributions to reionization and guiding future surveys.

Contribution

It provides empirical relations for the quasar UV luminosity function parameters over redshift and predicts quasar counts for upcoming surveys, enhancing understanding of their role in cosmic reionization.

Findings

Both double power-law and Schechter functions fit the data well.

Including faint AGNs increases quasars' contribution to reionization.

Predicted quasar counts will help constrain high-z quasar populations.

Abstract

We study the redshift evolution of the quasar UV Luminosity Function (LF) for 0.5 < z < 6.5, by collecting the most up to date observational data and, in particular, the recently discovered population of faint AGNs. We fit the QSO LF using either a double power-law or a Schechter function, finding that both forms provide good fits to the data. We derive empirical relations for the LF parameters as a function of redshift and, based on these results, predict the quasar UV LF at z=8. From the inferred LF evolution, we compute the redshift evolution of the QSO/AGN comoving ionizing emissivity and hydrogen photoionization rate. If faint AGNs are included, the contribution of quasars to reionization increases substantially. However, their level of contribution critically depends on the detailed shape of the QSO LF, which can be constrained by efficient searches of high-z quasars. To this aim, we predict the expected (i) number of z>6 quasars detectable by ongoing and future NIR surveys (as EUCLID and WFIRST), and (ii) number counts for a single radio-recombination line observation with SKA-MID (FoV = 0.49 deg^2) as a function of the Hnalpha flux density, at 0<z<8. These surveys (even at z<6) will be fundamental to better constrain the role of quasars as reionization sources.