2024/11/29 by Hiroto Yanagisawa, Yanagisawa, Hiroto, Masami Ouchi +19
Physics and Astronomy · #Stellar, planetary, and galactic studies #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies
paper · pdf · doi:10.48550/arxiv.2411.19893
We investigate UV continuum slopes β of 863 galaxies at z=4-14 using archival JWST/NIRSpec PRISM spectra obtained from major JWST GTO, ERS, and GO programs, including JADES, CEERS, and UNCOVER. Among these galaxies, we identify a remarkable galaxy at z=9.25, dubbed EBG-1, with a significantly blue UV slope β=-2.99±0.15, unlike the rest of the galaxies that exhibit red continua or ambiguous blue continua hindered by large uncertainties. We confirm that the β value negligibly changes by the data reduction and fitting wavelength ranges for UV emission/absorption line masking. The extreme blue slope, β=-3.0, rules out significant contributions from dust extinction or AGN activity. Comparing with stellar and nebular emission models, we find that such a blue UV slope cannot be reproduced solely by stellar models even with very young, metal-poor, or top-heavy contiguous star formation associated with strong nebular continua making the UV slopes red, but with a high ionizing photon escape fraction, fescion \gtrsim 0.5, for a weak nebular continuum. While the Hβ emission line is not detected, likely due to the limited sensitivity of the spectrum, we find moderately weak [O III] λλ4959,5007 emission lines for the given star-formation rate (3 M_\odot yr-1) and stellar mass (108.0 M_\odot) that are about three times weaker than the average emission lines, again suggestive of the high ionizing photon escape fraction, fescion ∼ 0.7 or more. EBG-1 would provide crucial insights into stellar and nebular continuum emission in high-redshift galaxies, serving as an example of the ionizing photon escaping site at the epoch of reionization.