Zapped then napped? A rapidly quenched remnant leaker candidate with a steep spectroscopic <i>β</i><sub>UV</sub> slope at z = 8.5
William Baker, Francesco D’Eugenio, R. Maiolino, Andrew J. Bunker, Charlotte Simmonds, Sandro Tacchella, Joris Witstok, Santiago Arribas, Stefano Carniani, Stéphane Charlot, Jacopo Chevallard, Mirko Curti, Emma Curtis-Lake, Gareth C. Jones, Nimisha Kumari, Pierluigi Rinaldi, Brant Robertson, Christina C. Williams, Chris J. Willott, Yongda Zhu
Abstract
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 2.9 σ detection of [OII] λλ 3726, 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.