Gas Dynamics of a Luminous z = 6.13 Quasar ULAS J1319+0950 Revealed by ALMA High-resolution Observations

Abstract

We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C II] 158 μm fine structure line emission toward a far-infrared-luminous quasar, ULAS J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of ~0."3, and resolve both the dust continuum and the [C II] line emission on a few kiloparsec scales. The [C II] line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the [C II]-emitting gas. The combined data confirm the [C II] velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the [C II] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 ± 55 km s−1 at a radius of 3.2 kpc with an inclination angle of 34°. We measure the dynamical mass within the 3.2 kpc region to be 13.4^(+7.8)_(-5.3) x 10^(10) M⊙. This yields a black-hole and host galaxy mass ratio of 0.020^(+0.013)_(-0.007), which is about 4^(+3)_(-2) times higher than that of the present-day M_(BH)/M_(bulge) ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe.

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