We present Atacama Large Millimeter/submillimeter Array observations of an intrinsically radio-bright ( L _ { 1.4 GHz } = ( 1.7 \pm 0.1 ) \times 10 ^ { 25 } W Hz ^ { -1 } ) and infrared luminous ( L _ { IR } \approx 10 ^ { 13 } L _ { \odot } ) galaxy at z = 2.6 .
The infrared-to-radio luminosity ratio , q = 1.8 , indicates the presence of a radio loud active galactic nucleus ( AGN ) .
Gravitational lensing by two foreground galaxies at z \approx 0.2 provides access to physical scales of approximately 360 pc , and we resolve a 2.5 kpc-radius ring of star-forming molecular gas , traced by atomic carbon C i . ( J = 1 \rightarrow 0 ) and carbon monoxide CO . ( J = 4 \rightarrow 3 ) .
We also detect emission from the cyanide radical , CN . ( N = 4 \rightarrow 3 ) .
With a velocity width of 680 km s ^ { -1 } , this traces dense molecular gas travelling at velocities nearly a factor of two larger than the rotation speed of the molecular ring .
While this could indicate the presence of a dynamical and photochemical interaction between the AGN and molecular interstellar medium on scales of a few 100 pc , on-going feedback is unlikely to have a significant impact on the assembly of stellar mass in the molecular ring , given the \sim 10s Myr depletion timescale due to star formation .