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

We investigate the prospects for discovering blazars at very high redshifts (z greater than or similar to 3-6) with the Fermi Gamma-ray Space Telescope (hereinafter 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 the Energetic Gamma-Ray Experiment Telescope and the 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, which is well-constrained up to z similar to 5. We find that the Fermi may discover a few blazars up to z similar to 6 in the entire sky during its 5-yr survey. We further discuss how such high-redshift blazar candidates may be efficiently selected in the future Fermi data.