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Title: X-ray properties of z > 4 blazars

Abstract

ABSTRACT We present the X-ray analysis of the largest flux-limited complete sample of blazar candidates at z > 4 selected from the Cosmic Lens All Sky Survey (CLASS). After obtaining a nearly complete (24/25) X-ray coverage of the sample (from Swift-XRT, XMM–Newton, and Chandra), we analysed the spectra in order to identify the bona fide blazars. We classified the sources based on the shape of their Spectral Energy Distributions and, in particular, on the flatness of the X-ray emission and its intensity compared to the optical one. We then compared these high-z blazars with a blazar sample selected at lower redshifts ($$\bar{z}\sim 1$$). We found a significant difference in the X-ray-to-radio luminosity ratios, with the CLASS blazars having a mean ratio 2.4 ± 0.5 times larger than low-z blazars. We tentatively interpret this evolution as due to the interaction of the electrons of the jet with the Cosmic Microwave Background photons, which is expected to boost the observed X-ray emission at high redshifts. Such a dependence has been already observed in highly radio loud AGNs in the recent literature. This is the first time it is observed using a statistically complete radio flux limited sample of blazars. We have then evaluated whether this effect could explain the differences in the cosmological evolution recently found between radio and X-ray selected samples of blazars. We found that the simple version of this model is not able to solve the tension between the two evolutionary results.

Authors:
 [1]; ORCiD logo [2];  [2];  [3];  [2]; ORCiD logo [4];  [5]
  1. INAF - Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milano, Italy, Dipartimento di Fisica G. Occhialini, Università di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
  2. INAF - Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milano, Italy
  3. INAF - Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milano, Italy, DiSAT, Università degli Studi dell’Insubria, Via Valleggio 11, I-22100 Como, Italy
  4. XMM-Newton Science Operations Centre, ESAC/ESA, PO Box 78, Villanueva de la Cañada, E-28691 Madrid, Spain
  5. Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, I-40127 Bologna, Italy, INAF - Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna, Italy
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1560758
Resource Type:
Published Article
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 489 Journal Issue: 2; Journal ID: ISSN 0035-8711
Publisher:
Oxford University Press
Country of Publication:
United Kingdom
Language:
English

Citation Formats

Ighina, L., Caccianiga, A., Moretti, A., Belladitta, S., Della Ceca, R., Ballo, L., and Dallacasa, D. X-ray properties of z > 4 blazars. United Kingdom: N. p., 2019. Web. https://doi.org/10.1093/mnras/stz2340.
Ighina, L., Caccianiga, A., Moretti, A., Belladitta, S., Della Ceca, R., Ballo, L., & Dallacasa, D. X-ray properties of z > 4 blazars. United Kingdom. https://doi.org/10.1093/mnras/stz2340
Ighina, L., Caccianiga, A., Moretti, A., Belladitta, S., Della Ceca, R., Ballo, L., and Dallacasa, D. Fri . "X-ray properties of z > 4 blazars". United Kingdom. https://doi.org/10.1093/mnras/stz2340.
@article{osti_1560758,
title = {X-ray properties of z > 4 blazars},
author = {Ighina, L. and Caccianiga, A. and Moretti, A. and Belladitta, S. and Della Ceca, R. and Ballo, L. and Dallacasa, D.},
abstractNote = {ABSTRACT We present the X-ray analysis of the largest flux-limited complete sample of blazar candidates at z > 4 selected from the Cosmic Lens All Sky Survey (CLASS). After obtaining a nearly complete (24/25) X-ray coverage of the sample (from Swift-XRT, XMM–Newton, and Chandra), we analysed the spectra in order to identify the bona fide blazars. We classified the sources based on the shape of their Spectral Energy Distributions and, in particular, on the flatness of the X-ray emission and its intensity compared to the optical one. We then compared these high-z blazars with a blazar sample selected at lower redshifts ($\bar{z}\sim 1$). We found a significant difference in the X-ray-to-radio luminosity ratios, with the CLASS blazars having a mean ratio 2.4 ± 0.5 times larger than low-z blazars. We tentatively interpret this evolution as due to the interaction of the electrons of the jet with the Cosmic Microwave Background photons, which is expected to boost the observed X-ray emission at high redshifts. Such a dependence has been already observed in highly radio loud AGNs in the recent literature. This is the first time it is observed using a statistically complete radio flux limited sample of blazars. We have then evaluated whether this effect could explain the differences in the cosmological evolution recently found between radio and X-ray selected samples of blazars. We found that the simple version of this model is not able to solve the tension between the two evolutionary results.},
doi = {10.1093/mnras/stz2340},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 2,
volume = 489,
place = {United Kingdom},
year = {2019},
month = {8}
}

Journal Article:
Free Publicly Available Full Text
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https://doi.org/10.1093/mnras/stz2340

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Cited by: 5 works
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