Kavli Affiliate: Debora Sijacki
| First 5 Authors: Francesco D’Eugenio, Roberto Maiolino, Michele Perna, Hannah Uebler, Xihan Ji
| Summary:
JWST spectroscopy has revealed a population of compact objects at redshifts
$z=2$-9 with `v’-shaped spectral energy distributions, broad permitted lines,
and, often, hydrogen Balmer absorption. Among these `Little Red Dots’ (LRDs),
Abell2744-QSO1 at $z=7.04$ has been confirmed to have time-variable equivalent
width (EW) in its broad emission lines, confirming its AGN nature. We extend
the analysis of NIRSpec/IFS data from the BlackTHUNDER survey to the H$alpha$
line. The broad-line profile in Abell2744-QSO1 is manifestly non-Gaussian,
requiring at least two Gaussian components with full width at half maximum
FWHM=$450pm50$ and $1800pm100$ km s$^{-1}$. Crucially, we also detect a
narrow-line Gaussian component, and strong H$alpha$ absorption (EW relative to
the continuum $approx 30^{+15}_{-9}$ A), confirming a connection between the
strong Balmer break and line absorption. The absorber is at rest with respect
to broad H$alpha$, suggesting that the gas cannot be interpreted as an inflow
or outflow, forming instead a long-lived structure. Its velocity dispersion is
$sigma_{abs} = 100pm10$ km s$^{-1}$, consistent with the value inferred from
the analysis of the Balmer break. Based on H$alpha$, we infer a black hole
mass of log(M$_{BH}$/M$_odot$)=6.3-6.7, 0.9-1.3 dex smaller than previous
estimates based on H$beta$. The Eddington ratio is 0.7-1.6. Combining the high
signal-to-noise ratio of the narrow H$alpha$ line with the spectral resolution
R=3,700 of the G395H grating, we infer a narrow-line dispersion $sigma_n =
22^{+5}_{-6}$ km s$^{-1}$, which places a stringent constraint on the
black-hole-to-dynamical-mass ratio of this system to be
M$_{BH}$/M$_{dyn}$>0.02-0.4. If M$_{BH}$ is near the low-mass end of our
estimates, the SMBH would be accreting at a super-Eddington rate.
Alternatively, at the high-M$_{BH}$ end, there would be minimal room for a host
galaxy.
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