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Arxiv: Fading Light, Fierce Winds: JWST Snapshot of a Sub-Eddington Quasar at Cosmic Dawn Published: 12/5/2024 9:00:02 PM Updated: 2/14/2025 10:44:55 PM

Paper abstract: The majority of most luminous quasars during the epoch of reionizationaccrete near or above the Eddington limit, marking the vigorous growth ofprimitive supermassive black holes (SMBHs). However, their subsequent evolutionand environmental impact remain poorly characterized. We present JWST/NIRSpecprism IFU observations of HSC J2239+0207, a low-luminosity quasar atz~6.25 likely in a late stage of mass assembly with an overmassive SMBHrelative to its host galaxy. Using H\beta and H\alpha broad emission lines,we estimate an SMBH mass M_{\rm BH}~3\times10^8~M_{\odot} and confirm itssub-Eddington accretion at \lambda_{\rm Edd}~0.4. Strong FeII emission anda proximity zone of typical size suggest a metal-rich, highly evolved system.In the far-UV, this quasar presents strong broad-absorption-line features,indicative of high-velocity winds (\nu~10^4~{\rm km/s}). Meanwhile,minimal dust reddening is inferred from the quasar continuum and broad-lineBalmer decrement, suggesting little dust along the polar direction. Mostinterestingly, we identify a gas companion ~5 kpc from the quasar with ahigh [OIII]/H\beta ratio (\gtrsim10), likely representing outflowing gasblown away by AGN feedback. These results highlight HSC J2239+0207 as a likelyfading quasar in transition, providing rare insights into SMBH evolution, AGNfeedback, and AGN-galaxy interactions in the early Universe.