PRISMS. UNCOVER-26185, a metal-poor SFG at z=10.05 with no evidence for a X-ray-luminous AGN
/ Authors
J. Álvarez-Márquez, L. Colina, A. Crespo-Gomez, S. Kendrew, J. Zavala, R. Marques-Chaves, C. Prieto-Jiménez, Abdurro’uf, C. Blanco-Prieto, L. Boogaard
and 25 more authors
M. Castellano, A. Fontana, Y. Fudamoto, S. Fujimoto, M. García-Marín, Y. Harikane, S. Harish, T. Hashimoto, T. Hsiao, E. Iani, A. Inoue, D. Langeroodi, R. Lin, J. Melinder, L. Napolitano, G. ¨Ostlin, P. Pérez-González, P. Rinaldi, B. Rodríguez, Del Pino, P. Santini, Y. Sugahara, T. Treu, A. Varo-O’ferral, G. Wright
/ Abstract
This work presents the first results of the PRImordial galaxy Survey with MIRI Spectroscopy (PRISMS), a JWST cycle 4 program (PID 8051) aimed at the characterization of a relatively large sample of ten galaxies about 500 Myr after the Big Bang. Here, we present deep (13.9 hours) spectroscopy with the MIRI LRS of the lensed galaxy UNCOVER-26185 at a redshift of z=10.054. It is a faint UV galaxy (UV absolut magnitude of -18.83 mag) previously identified as a X-ray luminous AGN. MIRI LRS detects the H$\beta$+[OIII]4960,5008 complex and H$\alpha$ emission line with a significance of 10$\sigma$ and 8$\sigma$, respectively, as well as the optical continuum emission at rest-frame 0.45 $\mu$m and 0.57 $\mu$m with a signal-to-noise ratio of 6-7. The UV-to-optical spectral energy distribution, combining continuum and emission lines, is compatible with: (i) a low stellar (A$_V$= 0.2) and nebular (A$_V$=0.0) extinction, (ii) a SFH composed by a young (7 Myr) starburst and an intermediate-age (65 Myr) stellar population, and (iii) a total stellar mass of 1.7$\times$10$^{8}$ M$_{\odot}$. The H$\alpha$-derived star-formation rate is 1.3 M$_{\odot}$ yr$^{-1}$. The low optical emission line ratios locate UNCOVER-26185 as the most metal-poor (Z = 0.04 Z$_{\odot}$), and as outlier with the lowest ionization (logU=-2.5) galaxy identified so far at redshifts above 9. With no evidence of an active galactic nuclei in the rest-frame UV-to-optical spectrum, UNCOVER-26185 has the properties of a metal-poor, main-sequence star-forming galaxy at redshift 10, with ISM and ionization properties very different than those of the already studied UV-bright galaxies at redshifts beyond 10. PRISMS is starting to explore the population of intermediate-UV luminosity galaxies at z=10, covering UV absolute magnitudes in the range of -17.9 to -20.5, fainter than those of UV-bright galaxies studied so far.