2024/08/07 by Francesco D’Eugenio, R. Maiolino, D'Eugenio, Francesco +31
Physics and Astronomy · #Gamma-ray bursts and supernovae #Astronomy and Astrophysical Research #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2408.03982
We present NIRSpec/MSA observations from the JWST large-area survey WIDE, targeting the rest-frame UV-optical spectrum of Ulema, a radio-AGN host at redshift z=4.6348. The low-resolution prism spectrum displays high equivalent width nebular emission, with remarkably high ratios of low-ionisation species of oxygen, nitrogen and sulphur, relative to hydrogen; auroral O+ emission is clearly detected, possibly also C+. From the high-resolution grating spectrum, we measure a gas velocity dispersion σ~400 km s-1, broad enough to rule out star-forming gas in equilibrium in the gravitational potential of the galaxy. Emission-line ratio diagnostics suggest that the nebular emission is due to a shock which ran out of pre-shock gas. To infer the physical properties of the system, we model simultaneously the galaxy spectral energy distribution (SED) and shock-driven line emission under a Bayesian framework. We find a relatively low-mass, star-forming system (M* = 1.4×1010 M_\odot, SFR = 70 M_\odot yr-1), where shock-driven emission contributes 50 per cent to the total Hβ luminosity. The nebular metallicity is near solar - three times higher than that predicted by the mass-metallicity relation at z=4.6, possibly related to fast-paced chemical evolution near the galaxy nucleus. We find no evidence for a recent decline in the SFR of the galaxy, meaning that, already at this early epoch, fast radio-mode AGN feedback was poorly coupled with the bulk of the star-forming gas; therefore, most of the feedback energy must end up in the galaxy halo, setting the stage for future quenching.