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 μm 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 Lyα line is redshifted by a velocity of 1035 ± 10 km s−1, marking the largest velocity offset between the [C ii] and Lyα 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 Lyα. 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 1013 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.