2025ApJ...980..121S

HSC 120505.09-000027.9 (J1205-0000) is one of the highest redshift (z = 6.72) dust-reddened quasars (red quasars) known to date. We present an improved analysis of Atacama Large Millimeter/submillimeter Array data of the [C II] 158 μm line and the underlying rest-frame far-infrared (FIR) continuum emission, previously reported in T. Izumi et al. (2021b), toward J1205-0000. Red quasars are thought to be a transitional phase from an obscured starburst to a luminous blue quasar, in some cases associated with massive outflows driven by the active galactic nucleus (AGN). J1205-0000 has a high FIR luminosity, L_FIR = 2.5 × 10¹²L_⊙ and a total IR luminosity of L_TIR = 3.5 × 10¹²L_⊙, corresponding to a star formation rate of ∼528M_⊙ yr^–1. With the [C II]-based dynamical mass of ∼1 × 10¹¹M_⊙, we conclude that J1205-0000 is hosted by a starburst galaxy. In contradiction to T. Izumi et al., our improved analysis shows no hint of a broad component in the [C II] line spectrum. Thus there is no evidence for a host galaxy-scale fast [C II] outflow, despite the fact that J1205-0000 has fast nuclear ionized outflows seen in the rest-frame UV. We explore several scenarios for this discrepancy (e.g., the early phase of AGN feedback, reliability of the [C II] line as a tracer of outflows), and we claim that it is still too early to conclude that there is no significant negative AGN feedback on star formation in this red quasar.