Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Matilde Brazzini, Matilde Brazzini, , ,
| Summary:
The majority of Little Red Dots (LRDs) hosting Active Galactic Nuclei (AGN)
exhibits broad H$alpha$ emission, which recent studies propose originates from
scattering off free electrons within an ionized and dense medium embedding the
Broad Line Region (BLR), rather than directly from the BLR itself. This model
suggests that the observed broad lines may be intrinsically narrower than
observed, which would lead to black hole masses that are up to two orders of
magnitude smaller than what inferred when assuming that the whole broad line
comes from the BLR. To test this model, we present a joint analysis of multiple
hydrogen recombination lines in the ”Rosetta Stone”AGN, the brightest known
LRD at $z$=2.26. We show that H$alpha$, H$beta$ and Pa$beta$ have different
spectral profiles, which is inconsistent with the predictions of the simple
electron scattering scenario. Additionally, we test a variety of exponential
models and show that none of them can simultaneously reproduce all three line
profiles with physically plausible parameters. The inadequacy of these models
for the Rosetta Stone implies that the scenario of electron scattering by an
ionized medium surrounding the BLR is not universally applicable to LRDs and
AGN, and therefore provides a counterexample to the claim of a universal and
systematic overestimation of black hole masses.
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