Resolving the Interstellar Medium in the Nuclear Region of Two z = 5.78 Quasar Host Galaxies with ALMA

Abstract

We present ALMA observations of the [C II] 158 μm fine structure line and dust continuum emission from two quasars, SDSS J104433.04−012502.2 and SDSS J012958.51−003539.7, at z = 5.78. The ALMA observations at 0."2 resolution map the dust and gas on kiloparsec scales. The spatially resolved emission shows a similar trend of decreasing [C II]–far-infrared (FIR) ratios with increasing FIR surface brightnesses as was found in the infrared luminous galaxies with intense star formation. We confirm the velocity gradients of [C II] emission found previously in SDSS J0129−0035. No clear evidence of order motion is detected in SDSS J1044−0125. The velocity maps and position–velocity diagrams also suggest turbulent gas clumps in both objects. We tentatively detect a [C II] peak offset 4.9 kpc to the east of SDSS J1044−0125. This may be associated with an infalling companion, or node of gas outflow. All these results suggest significant dynamical evolution of the interstellar medium in the nuclear region of these young quasar-starburst systems. We fit the velocity map of the [C II] emission from SDSS J0129−0035 with a rotating disk model. The result suggests a face-on system with an inclination angle of 16° ± 20° and constrains the lower limit of the host galaxy dynamical mass to be 2.6 × 10¹⁰ M ⊙ within the [C II] emitting region. It is likely that SDSS J0129−0035, as well as other young quasars with supermassive black hole masses on the order of 10⁷ M⊙ to 10⁸ M⊙, falls close to the black hole and host galaxy mass relation defined by local galaxies.

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