An ALMA Band 7 survey of SDSS/ Herschel quasars in Stripe 82. II. The nature of FIR-bright quasars

Abstract

We investigated the star formation properties and UV/optical spectral characteristics of 142 far-infrared (FIR)-bright quasars at redshifts 1 łe z łe 4 to probe supermassive black hole (SMBH) and host galaxy co-evolution. By combining multi-wavelength observations with high-resolution ALMA sub-millimetre (submm) data, we overcame source confusion and robustly constrained star formation rates (SFRs). The inclusion of ALMA data in the spectral energy distribution fitting reduces SFR estimates by ∼20% for quasars with single submm counterparts and by a factor of ge2 for FIR-blended multi-component systems, while reducing FIR luminosity uncertainties by ∼18%. The revised host SFRs span 500 to 3000 $ (median 1080 ), confirming these systems are extreme starbursts. The very shallow positive correlation between starburst and accretion luminosities suggests that SMBH accretion and star formation in the host are not coupled on the timescales probed by the observations. Compared to the general population of FIR-faint quasars, FIR-bright sources have factor of 3 higher detection rates at 1.4 GHz, predominantly following the FIR--radio correlation, and reduced yr -1 yr$^ -1 and equivalent widths with largely unchanged, suggesting active galactic nuclei--driven winds that have little impact on Together, these results place FIR-bright quasars in a brief transitional phase that bridges heavily obscured `blowout' galaxies and optically unobscured blue quasars, where bulge assembly and SMBH growth peak simultaneously during ongoing stellar assembly.