Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Francesco D’Eugenio, Ignas Juodžbalis, Xihan Ji, Jan Scholtz, Roberto Maiolino
| Summary:
We present a broad-line active galactic nucleus (AGN) at z = 5.077, observed
with both NIRSpec/MSA and NIRSpec/IFU by the JADES and BlackTHUNDER surveys.
The target exhibits all the hallmark features of a ‘Little Red Dot’ (LRD) AGN.
The combination of spatially resolved and high-resolution spectroscopy offers
deeper insight into its nature. The H$alpha$ line has multiple components,
including two broad Gaussians, yielding a black-hole mass of $log(M_{rm
BH}/M_odot) = 7.65$, while the narrow [O III]$lambda$5007 gives a galaxy
dynamical mass of $log(M_{rm dyn}/M_odot) = 9.1$, suggesting a dynamically
overmassive black hole relative to the host galaxy. The target has two
satellites, and is immersed in a 7-kpc wide pool of ionized gas. A spatially
detached outflow is also tentatively detected. H$alpha$ shows strong
absorption with high equivalent width (EW), ruling out a stellar origin, and
with velocity and velocity dispersion of v = -13 km s$^{-1}$ and $sigma$ = 120
km s$^{-1}$. There is tentative evidence (2.6 $sigma$) of temporal variability
in the EW of the H$alpha$ absorber over two rest-frame months. If confirmed,
this would suggest a highly dynamic environment. Notably, while the H$alpha$
absorber is clearly visible and even dominant in the high-resolution G395H
observations, it is not detected in the medium-resolution G395M data of the
same epoch. This implies that the current incidence rate of absorbers in LRDs –
and especially of rest-frame absorbers – may be severely underestimated,
because most LRDs rely on lower-resolution spectroscopy. In this context, the
high incidence rate of rest-frame absorbers in LRDs may indicate a
configuration that is either intrinsically stationary, such as a rotating disc,
or that exhibits time-averaged stability, such as an oscillatory ‘breathing
mode’ accretion of cyclic expansion and contraction of the gas around the SMBH.
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