Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Francesco D’Eugenio, Roberto Maiolino, Vijay H. Mahatma, Giovanni Mazzolari, Stefano Carniani
| Summary:
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 $sigma$~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$times$10^{10} M$_odot$, SFR = 70 M$_odot$ yr$^{-1}$), where shock-driven
emission contributes 50 per cent to the total H$beta$ 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.
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