2019ApJ...879..117K

Recent simulation studies suggest that the supermassive black hole (SMBH) growth in the early universe may precede prolonged intense star formation within its host galaxy, rather than quasars appearing after the obscured dusty star formation phase. If so, high-redshift quasars with low Eddington ratios (λ_Edd) would be found in actively star-forming hosts with a star formation rate (SFR) of >100 M_☉ yr^–1. We present the submillimeter observations of IMS J2204+0112, a faint quasar with a quasar bolometric luminosity of L_bol=4.2×10¹²L_☉ and a low λ_Edd of only 0.1 at z ∼ 6, carried out with the Atacama Large Millimeter/submillimeter Array (ALMA). From its submillimeter fluxes, we measure the rest-frame far-infrared (FIR) luminosity of L_FIR=(3-4)×10¹²L_☉. Interestingly, the derived host galaxy's SFR is ∼500-700M_☉ yr^–1, an order of magnitude higher than those of the L_bol-matched z >= 6 quasars with high λ_Edd. Similar FIR excesses are also found for five z >= 6 low-λ_Edd quasars (λ_Edd< 0.2) in the literature. We show that the overall SFR, M_BH, and λ_Edd distributions of these and other submillimeter-detected quasars at z >= 6 can be explained with the evolutionary track of high-redshift quasars in a simulation study, where low λ_Edd and high SFR quasars are expected at the end of the SMBH growth. This suggests that the nuclear activities of the low λ_Edd, high L_FIR quasars are on the brink of being turned off, while their host galaxies continue to form the bulk of their stars at SFR >100 M_☉ yr^–1.