Heavily Obscured AGN detection: a Radio vs X-ray challenge
Journal
Date Issued
2024
Author(s)
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Brusa, Marcella
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Marco Chiaberge
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Quirino D'Amato
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Kazushi Iwasawa
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Colin Norman
Abstract
In this work, we study the AGN radio detection effectiveness in the major
deep extragalactic surveys, considering different AGN obscuration levels,
redshift, and AGN bolometric luminosities. We particularly focus on comparing
their radio and X-ray detectability, making predictions for present and future
radio surveys. We extrapolate the predictions of AGN population synthesis model
of cosmic X-ray background (CXB) to the radio band, by deriving the 1.4 GHz
luminosity functions of unobscured (i.e. with hydrogen column densities $\log
N_{H} <22$), obscured ($22<\log N_{H}<24$) and Compton-thick (CTK, $\log N_{H}
>24$) AGN. We then use these functions to forecast the number of detectable AGN
based on the area, flux limit, and completeness of a given radio survey and
compare it with the AGN number resulting from X-ray predictions. When applied
to deep extragalactic fields covered both by radio and X-ray observations, we
show that, while X-ray selection is generally more effective in detecting
unobscured AGN, the surface density of CTK AGN radio detected is on average
$\sim 10$ times larger than the X-ray one, and even greater at high redshifts,
considering the current surveys and facilities. Our results suggest that
thousands of CTK AGN are already present in current radio catalogs, but most of
them escaped any detection in the corresponding X-ray observations. We also
present expectations for the number of AGN to be detected by the Square
Kilometer Array Observatory (SKAO) in its future deep and wide radio continuum
surveys, finding that it will be able to detect more than 2000 AGN at $z>6$ and
some tens at $z>10$, more than half of which are expected to be CTK.
Volume
687
Start page
A120
Issn Identifier
0004-6361
Rights
open.access
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