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

TL;DR

This study analyzes X-ray observations of 15 young radio quasars at high redshift, revealing their spectral properties, luminosities, and correlations across wavelengths, and identifying notable outliers including a potential Compton-thick source.

Contribution

First comprehensive X-ray analysis of young radio quasars at z > 4.5, providing insights into their spectral characteristics and multiwavelength correlations.

Findings

Average photon index is 1.5±0.1.

Luminosities range from 0.5 to 23.2 × 10^{45} erg s^{-1}.

Detected correlation between radio and X-ray luminosities.

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 $1.5\pm0.1$. Unabsorbed rest-frame $2-10$ keV luminosities are found to range between $(0.5-23.2) \times 10^{45}$ erg s$^{-1}$. The optical-X-ray power-law spectral index $\alpha_{ox}$ is calculated for each source using optical/UV data available in the literature. The $\alpha_{ox}$-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.