A Magnified View of Circumnuclear Star Formation and Feedback around an Active Galactic Nucleus at z = 2.6

We present Atacama Large Millimeter/submillimeter Array observations of an intrinsically radio-bright (L _{1.4 GHz} = (1.7 ± 0.1) ×10 ²⁵ W Hz ^-1) and infrared luminous (L _IR ≈ 10 ¹³ L _o) 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 ≈ 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 (1 → 0) and carbon monoxide CO (J = 4 → 3). We also detect emission from the cyanide radical, CN (N = 4 → 3). With a velocity width of 680 km s ^-1, this traces dense molecular gas traveling 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, ongoing feedback is unlikely to have a significant impact on the assembly of stellar mass in the molecular ring, given the ∼10 s Myr depletion timescale due to star formation.