Kavli Affiliate: Roberto Maiolino
| First 5 Authors: William M. Baker, Francesco D’Eugenio, Roberto Maiolino, Andrew J. Bunker, Charlotte Simmonds
| Summary:
We use NIRSpec MSA spectroscopy and NIRCam Photometry to explore the
properties of JADES-GS8-RL-1, a rapidly quenched, $z=8.5$ galaxy with a stellar
mass of $10^{8.9}M_odot$, a steep blue UV slope, a Balmer break, and no sign
of strong emission lines. With a $beta_{UV}$=-2.8$pm 0.2$, as measured from
the NIRSpec spectrum, JADES-GS8-RL-1 is consistent with negligible dust
attenuation and little to no contribution from the nebular continuum alongside
a probable high escape fraction. The $beta_{UV}$ slope measured from
photometry varies from -3.0 in the central regions to -2.2 at the outskirts
suggesting possible regional differences in the escape fraction. There are no
high-ionisation emission lines, only a tentative 2.9sig detection of [OII].
Using photometry, this emission appears to be extended, possibly corresponding
to weakly ionised gas expelled during or after the quenching process.
JADES-GS8-RL-1 is spatially resolved with a half-light radius of 240 pc and has
an exponential, disc-like morphology. It appears to have formed all its stars
in a short burst within the past 100 Myr with a formation time of $approx$70
Myr and a quenching time of $approx$30 Myr. This quenching would have occurred
rapidly, making it a more distant example of the kind of low-mass
"mini-quenched" galaxies previously observed at high-z. Due to the extremely
blue $beta_{UV}$ slope, our best-fit model predicts a high value for fesc of
>10%, consistent with the value derived from the $beta_{UV}$ slope, which
when combined with our extraordinarily low O32 upper limit suggests
JADES-GS8-RL-1 is a fascinating example of a high-z "remnant leaker" in one of
its earliest phases, deep in the epoch of reionisation.
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