Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Pierluigi Rinaldi, Pablo G. Pérez-González, George H. Rieke, Jianwei Lyu, Francesco D’Eugenio
| Summary:
We present a comprehensive analysis of the MIRI Extremely Red Object Virgil,
a Lyman-$alpha$ emitter at $z_{spec} = 6.6379 pm 0.0035$ with the photometric
properties of a Little Red Dot. Leveraging new JWST/MIRI imaging from the MIDIS
and PAHSPECS programs, we confirm Virgil’s extraordinary nature among galaxies
in JADES/GOODS-South, exhibiting a strikingly red NIRCam-to-MIRI color (F444W
$-$ F1500W = $2.84pm0.04$ mag). Deep NIRSpec/PRISM spectroscopy from the OASIS
program offers key insights into the host galaxy, revealing properties of an
average star-forming galaxy during Cosmic Reionization, such as a subsolar
metallicity, low-to-moderate dust content, and a relatively high ionization
parameter and electron temperature. By estimating the star formation rate of
Virgil from UV and H$alpha$, we find evidence that the galaxy is either
entering or fading out of a bursty episode. Although line-ratio diagnostics
employed at high-$z$ would classify Virgil as an Active Galactic Nucleus (AGN),
this classification becomes ambiguous once redshift evolution is considered.
Nonetheless, Virgil occupies the same parameter space as recently confirmed
AGNs at similar redshifts. The new deep MIRI data at 15 $mu$m reinforce the
AGN nature of Virgil, as inferred from multiple spectral energy distribution
(SED) fitting codes. Virgil’s rising infrared SED and UV excess resemble those
of Dust-Obscured Galaxies (DOGs) studied with Spitzer at Cosmic Noon,
particularly blue-excess HotDOGs. Our results highlight the need for a
multi-wavelength approach incorporating MIRI to uncover such extreme sources at
$zgtrsim6$ and to shed light on the interplay between galaxy evolution and
early black hole growth during Cosmic Reionization.
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