Kavli Affiliate: John D. Silverman
| First 5 Authors: Wenke Ren, Wenke Ren, , ,
| Summary:
We present a systematic search for broad-line active galactic nuclei (AGNs)
in the ALPINE-CRISTAL-JWST sample of 18 star-forming galaxies
($M_star>10^9.5~M_odot$) at redshifts $z=4.4-5.7$. Using JWST/NIRSpec
IFU, we identify 7 AGN candidates through the detection of broad Ha emission
lines from 33 aperture spectra centred on photometric peaks. These candidates
include one highly robust AGN detection with FWHM $sim$ 2800 kms and six
showing broad components with FWHM $sim 600-1600$ kms, with two in a merger
system. We highlight that only broad-line detection is effective since these
candidates uniformly lie within narrow emission-line ratio diagnostic diagrams
where star-forming galaxies and AGNs overlap. The broad-line AGN fraction
ranges from 5.9% to 33%, depending on the robustness of the candidates.
Assuming that the majority are AGNs, the relatively high AGN fraction is likely
due to targeting high-mass galaxies, where simulations demonstrate that
broad-line detection is more feasible. Their black hole masses range from
$10^6$ to $10^7.5~M_odot$ with $0.1 lesssim L_rm bol/L_rm
Eddlesssim 1$. Counter to previous JWST studies at high redshift that found
overmassive black holes relative to their host galaxies, our candidates lie
close to or below the local $M_rm BH-M_star$ scaling relations, thus
demonstrating the effect of selection biases. This study provides new insights
into AGN-host galaxy co-evolution at high redshift by identifying faint
broad-line AGNs in galaxy samples, highlighting the importance of considering
mass-dependent selection biases and the likelihood of a large population of
AGNs being undermassive and just now being tapped by JWST.
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