Blazars at the Cosmic Dawn

The uncharted territory of the high-redshift (z greater than or similar to 3) universe holds the key to understanding the evolution of quasars. In an attempt to identify the most extreme members of the quasar population, that is, blazars, we have carried out a multiwavelength study of a large sample of radio-loud quasars beyond z = 3. Our sample consists of nine gamma-ray-detected blazars and 133 candidate blazars selected based on the flatness of their soft X-ray spectra (0.3-10 keV photon index <= 1.75), including 15 with Nuclear Spectroscopic Telescope Array (NuSTAR).observations. The application of the likelihood profile stacking technique reveals that the high-redshift blazars are faint gamma-ray emitters with steep spectra. The high-redshift blazars host massive black holes (< log M-BH,M- M circle dot > > 9) and luminous accretion disks (< L-disk > > 10(46) erg s(-1)). Their broadband spectral energy distributions are found to be dominated by high-energy radiation, indicating their jets are among the most luminous ones. Focusing on the sources exhibiting resolved X-ray jets (as observed with the Chandra satellite), we find the bulk Lorentz factor to be larger with respect to other z > 3 blazars, indicating faster moving jets. We conclude that the presented list of high-redshift blazars may act as a reservoir for follow-up observations, such as with NuSTAR, to understand the evolution of relativistic jets at the dawn of the universe.