X-Ray Properties of Young Radio Quasars at z > 4.5

Abstract

We present a comprehensive analysis of Chandra X-ray observations of 15 young radio quasars at redshifts 4.5 <  z  < 5.0. All sources are detected in the 0.5–7.0 keV energy band. Emission spectra are extracted, and the average photon index for the sample is measured to be 1.5 ± 0.1. Unabsorbed rest-frame 2–10 keV luminosities are found to range between (0.5–23.2) × 10 45 erg s −1 . The optical–X-ray power-law spectral index is calculated for each source using optical/UV data available in the literature. The –UV relationship is compared with other quasar surveys, and an anticorrelation is observed that agrees with independent estimates. Rest-frame radio and X-ray luminosities are established for the sample, and a correlation between the luminosities is detected. These multiwavelength results reinforce a lack of spectral evolution for quasars over a broad redshift range. We additionally identify three quasars from our multiwavelength analysis that are statistically significant outliers, with one source being a Compton-thick candidate in the early universe, and discuss each in detail.