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

Bradford Snios, Aneta Siemiginowska, Małgosia Sobolewska, C. C. Cheung, Vinay Kashyap, Giulia Migliori, Daniel A. Schwartz, Łukasz Stawarz, Diana M. Worrall

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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 anti-correlation 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.
Original languageEnglish
Article number127
Number of pages10
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 20 Aug 2020

Bibliographical note

Accepted to ApJ, 13 pages, 5 figures, 4 tables


  • astro-ph.HE


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