Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Andrea Comastri, Andrea Comastri, , ,
| Summary:
One of the most puzzling properties of the high-redshift AGN population
recently discovered by JWST, including both broad-line and narrow-line sources,
is their X-ray weakness. With very few exceptions, and regardless of the
optical classification, they are undetected at the limits of the deepest
Chandra fields, even when stacking signals from tens of sources in standard
observed-frame energy intervals (soft, hard, and full bands). It has been
proposed that their elusive nature in the X-ray band is due to heavy absorption
by dust-free gas or intrinsic weakness, possibly due to high, super-Eddington
accretion. In this work, we perform X-ray stacking in three customized
rest-frame energy ranges (1-4, 4-7.25, and 10-30 keV) of a sample of 50 Type 1
and 38 Type 2 AGN identified by JWST in the CDFS and CDFN fields. For the Type
2 sub-sample, we reach a total of about 210 Ms exposure, and we report a
significant ($sim 3sigma$) detection in the hardest (10-30 keV rest frame)
band, along with relatively tight upper limits in the rest frame softer energy
bands. The most straightforward interpretation is in terms of heavy obscuration
due to gas column densities well within the Compton thick regime ($> 2 times
10^24 $cm$^-2$) with a large covering factor, approaching 4$pi$. The same
procedure applied to the Type 1 sub-sample returns no evidence for a
significant signal in about 140 Ms stacked data in any of the adopted bands,
confirming their surprisingly elusive nature in the X-ray band obtained with
previous stacking experiments. A brief comparison with the current observations
and the implications for the evolution of AGN are discussed.
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