No galaxy-scale [CII] outflow detected in a z=6.72 red quasar with ALMA

ABSTRACT :
It has been claimed that active galactic nucleus (AGN)-driven massive outflows, occurring during a transition phase from an obscured dusty quasar to a normal blue quasar, are a key physical process in driving the co-evolution of galaxies and supermassive black holes (SMBHs). Partially dust-obscured red quasars are thought to represent the intermediate phase of this transition. However, while many blue quasars at z = 6-7 have been discovered in recent years, identifying red quasars at that epoch remains challenging due to their apparent faintness. Thus, deep, wide-area surveys and subsequent multi-wavelength follow-up observations are required to identify such red objects and test this evolutionary scenario. Here, we report on our ALMA Cycle 7 observations of the z = 6.72 red quasar HSC J120505.09−000027.9 (J1205−0000). This red quasar was initially identified by our deep Subaru Hyper Suprime-Cam (HSC) survey. It is apparently faint but intrinsically as luminous as -24.4 mag at rest-UV and hosts a massive black hole of 2.2 × 10^9 Msun. It is also known to be an N V and C IV BAL object, indicating the presence of nuclear outflows. We successfully detected both the [CII] 158 μm line and the underlying rest-FIR continuum emission (resolution ~0.6", 1σ ~ 0.1 mJy/beam at dV = 75 km/s). The continuum is very bright, with an estimated luminosity of 2.3 × 10^12 Lsun (equivalent to a star formation rate of ~485 Msun/yr), suggesting that the host galaxy of this red quasar is indeed a starburst system. Furthermore, regarding the AGN feedback, our observations do not conclusively assert the presence of [CII] outflows (the ratio of AGN bolometric luminosity to kinetic energy per unit time derived from the 3-sigma upper limit is 0.01%). These results suggest that this red quasar can be positioned in the early phase of the galaxy merger-induced evolution model.