Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Greta Zucchi, Greta Zucchi, , ,
| Summary:
Observations with the James Webb Space Telescope (JWST) have uncovered a
substantial population of high-redshift, broad-line active galactic nuclei
(AGNs), whose properties challenge standard models of black hole growth and AGN
emission. We analyze a spectroscopic sample of 34 Type 1 AGNs from the JWST
Advanced Deep Survey (JADES) survey, spanning redshifts 1.7 < z < 9, to
constrain the physical nature of the accretion flows powering these sources
with broad-line diagnostics statistically for the first time. At z > 5, we find
a marked suppression of high-ionization emission lines (HeII, CIV, NV) relative
to prominent broad Halpha and narrow [OIII] features. This contrast places
strong constraints on the shape of the ionizing spectral energy distribution
(SED) and on the physical conditions in the broad-line region (BLR). By
comparing the observations to photoionization models based on SEDs of black
holes accreting at sub-Eddington ratios, we show that standard AGN continua
struggle to reproduce the observed broad line ratios and equivalent widths
across a wide ionization parameter range. These results suggest the need for
modified SEDs — either intrinsically softened due to super-Eddington accretion
or radiative inefficiencies in the innermost disk, or externally filtered by
intervening optically thick gas that absorbs or scatters the highest-energy
photons before they reach the BLR.
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