Searching for the most distant blazars with the Fermi Gamma-ray Space Telescope

TL;DR

This paper assesses the potential for the Fermi Gamma-ray Space Telescope to discover extremely distant blazars at redshifts greater than 3, using an evolved gamma-ray luminosity function model informed by X-ray and quasar data.

Contribution

It introduces an extended high-redshift evolution model for blazars based on SDSS quasar data, predicting Fermi's capability to detect blazars up to z~6.

Findings

Fermi could discover a few blazars up to z~6 within 5 years.

The model aligns with existing EGRET and Fermi observations.

Strategies for selecting high-redshift blazar candidates are discussed.

Abstract

We investigate the prospects for discovering blazars at very high-redshifts (z>3-6) with the Fermi Gamma-Ray Space Telescope (Fermi), employing a model for the evolving gamma-ray luminosity function (GLF) of the blazar population. Our previous GLF model is used as a basis, which features luminosity-dependent density evolution implied from X-ray data on active galactic nuclei, as well as the blazar sequence paradigm for their spectral energy distribution, and which is consistent with EGRET and current Fermi observations of blazars.Here we augment the high-redshift evolution of this model by utilizing the luminosity function of quasars from the Sloan Digital Sky Survey (SDSS), which is well-constrained up to z~5. We find that Fermi may discover a few blazars up to z~6 in the entire sky during its 5-year survey. We further discuss how such high-redshift blazar candidates may be efficiently selected in future Fermi data.