Ongoing and fossil outflows detected in a high-redshift radio galaxy: [CII] observations of TN J0924−2201 at z = 5.17

ABSTRACT :
We present ALMA 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 identified a redshifted substructure of [C II] with a velocity of 702 ± 17 km s−1, which is close to the redshift of the CIV 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 non-detection 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 AGN is the most plausible interpretation, and they may exceed the escape velocity of a 10^13 Msun halo. These results collectively suggest that TN J0924−2201, with the 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.