Study of the gamma-Ray Radiation Properties of High-redshift Blazars at z>2.5

TL;DR

This study analyzes gamma-ray properties of 30 high-redshift blazars ($z>2.5$) over 15 years, revealing spectral curvature, luminosity differences, and insights into emission regions and jet-accretion relationships.

Contribution

It provides the first comprehensive spectral analysis of high-redshift blazars using Fermi-LAT data and models their emission mechanisms, highlighting the location of gamma-ray emission regions.

Findings

High-redshift blazars have higher gamma-ray luminosities and softer spectra.

Infrared seed photons better explain gamma-ray emission than broad-line region photons.

High-redshift blazars show higher jet power and lower IC peak frequencies.

Abstract

We study a sample of 30 high-redshift blazars ($z>2.5$) by means of spectra and the radiation mechanism with Fermi Large Area Telescope $\gamma$-ray observations spanning 15 years. Three models -- the power law, power law with an exponential cutoff, and log-parabola -- are employed to analyze the spectral properties, and most sources exhibit significant curvature. The high-redshift blazars exhibit higher $\gamma$-ray luminosities and softer spectral indices compared with their low-redshift counterparts, where B3~1343+451 has the highest integrated flux, $\rm 1.13 \times 10^{-7} \mathrm{\ ph \ cm^{-2} s^{-1}}$. We use a standard one-zone leptonic emission model to reproduce the spectral energy distributions of 23 sources with multiwavelength observations. We find that modeling with infrared seed photons is systematically better than with broad-line region (BLR) photons based on a $\chi^2$ test, which suggests that the $\gamma$-ray-emitting regions are most likely located outside the BLR. The fit results show that high-redshift blazars exhibit higher energy density, jet power, kinetic power, and accretion disk luminosities, along with lower synchrotron and inverse Compton (IC) peak frequencies, relative to their lower-redshift counterparts. We find that blazars with higher accretion disk luminosities tend to have lower IC peak frequencies, leading to more efficient cooling of high-energy electrons. The positive correlation between jet power and accretion disk luminosity further supports the possibility of an accretion-jet connection in these high-redshift sources.