Zapped then Napped? A rapidly quenched remnant leaker candidate with a steep spectroscopic $β_{UV}$ slope at z=8.5

We used 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, a steep blue UV slope, a Balmer break, and no sign of strong emission lines. With a β UV = −2.8 ± 0.2, as measured from the NIRSpec spectrum, JADES-GS8-RL-1 is consistent with having a negligible dust attenuation and little to no contribution from the nebular continuum alongside a probable high escape fraction. The β 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 2.9σ detection of [OII]λλ3726, 29. 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 of its stars in a short burst within the past 100 Myr with a formation time of ≈70 Myr and a quenching time of ≈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 β UV slope, our best-fit model predicts a high value for f esc of >10%, consistent with the value derived from the β 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.