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  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
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Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/28994
Title: The space density of z>4 blazars
Authors: CACCIANIGA, Alessandro 
MORETTI, Alberto 
Belladitta, S.
DELLA CECA, Roberto 
Antón, S.
Ballo, L.
Cicone, C.
Dallacasa, Daniele 
GARGIULO, ADRIANA 
Ighina, L.
Marchã, M. J.
SEVERGNINI, Paola 
Issue Date: 2019
Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 
Number: 484
Issue: 1
First Page: 204
Abstract: High-redshift blazars are an important class of active galactic nuclei (AGN) that can provide an independent estimate of the supermassive black hole mass function in high-redshift radio-loud AGN without the bias due to absorption along the line of sight. Using the Cosmic Lens All Sky Survey (CLASS), we built a complete radio flux-limited sample of high-redshift (z > 4) blazars suitable for statistical studies. By combining dedicated optical observations and the SDSS spectroscopic database, we obtained a sample of 26 blazar candidates with a spectroscopic redshift above 4. On the basis of their radio spectrum, we distinguish between blazars and QSO with a Gigahertz Peaked Spectrum (GPS) like spectrum. Out of the 18 confirmed blazars 14 constitute a completely identified, flux-limited sample down to a magnitude of 21 (AB). Using this complete sample, we derive a space density of blazars with 4 < z < 5.5 of ρ = 0.13^{+0.05}_{-0.03} Gpc^-3 This is the first actual estimate of the blazar space density in this range of redshift. This value is in good agreement with the extrapolation of the luminosity function and cosmological evolution based on a sample of flat-spectrum radio quasars selected at lower redshifts and it is consistent with a cosmological evolution peaking at z ∼ 2 similar to radio-quiet QSO. We do not confirm, instead, the presence of a peak at z ∼ 4 in the space density evolution, recently suggested using an X-ray selected sample of blazars. It is possible that this extreme peak of the evolution is present only among the most luminous blazars.
URI: http://hdl.handle.net/20.500.12386/28994
URL: https://academic.oup.com/mnras/article-abstract/484/1/204/5270742?redirectedFrom=fulltext
ISSN: 0035-8711
DOI: 10.1093/mnras/sty3526
Bibcode ADS: 2019MNRAS.484..204C
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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