Ongoing and Fossil Large-scale Outflows Detected in a High-redshift Radio Galaxy: [C ii] Observations of TN J0924-2201 at z = 5.174

Abstract

We present Atacama Large Millimeter/submillimeter Array observations of the [C ii ] 158 μ m line and the underlying continuum emission of TN J0924−2201, which is one of the most distant known radio galaxies at z > 5. The [C ii ] line and 1 mm continuum emission are detected at the host galaxy. The systemic redshift derived from the [C ii ] line is z _[C _II _] = 5.1736 ± 0.0002, indicating that the Ly α line is redshifted by a velocity of 1035 ± 10 km s ^−1 , marking the largest velocity offset between the [C ii ] and Ly α lines recorded at z > 5 to date. In the central region of the host galaxy, we identify a redshifted substructure of [C ii ] with a velocity of 702 ± 17 km s ^−1 , which is close to the C iv line with a velocity of 500 ± 10 km s ^−1 . The position and the velocity offsets align with a model of an outflowing shell structure, consistent with the large velocity offset of Ly α . The nondetection of [C ii ] and dust emission from the three CO(1–0)-detected companions indicates their different nature compared to dwarf galaxies, based on the photodissociation region model. Given their large velocity of ∼1500 km s ^−1 , outflowing molecular clouds induced by the active galactic nucleus are the most plausible interpretation, and they may exceed the escape velocity of a 10 ^13 M _⊙ halo. These results suggest that TN J0924−2201, with ongoing and fossil large-scale outflows, is in a distinctive phase of removing molecular gas from a central massive galaxy in an overdense region in the early Universe. A dusty H i absorber at the host galaxy is an alternative interpretation.

Keywords

• High-redshift galaxies
• Radio galaxies
• Radio active galactic nuclei
• AGN host galaxies