Black Holes in the Shadow: The Missing High-Ionization Lines in the Earliest JWST AGNs
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arXiv
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2025
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| author | Zucchi, Greta Ji, Xihan Madau, Piero Maiolino, Roberto Juodžbalis, Ignas D'Eugenio, Francesco Geris, Sophia Isobe, Yuki |
| author_facet | Zucchi, Greta Ji, Xihan Madau, Piero Maiolino, Roberto Juodžbalis, Ignas D'Eugenio, Francesco Geris, Sophia Isobe, Yuki |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_10772 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Black Holes in the Shadow: The Missing High-Ionization Lines in the Earliest JWST AGNs Zucchi, Greta Ji, Xihan Madau, Piero Maiolino, Roberto Juodžbalis, Ignas D'Eugenio, Francesco Geris, Sophia Isobe, Yuki Astrophysics of Galaxies 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. |
| title | Black Holes in the Shadow: The Missing High-Ionization Lines in the Earliest JWST AGNs |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2510.10772 |