2022ApJ...937..106C

We present the discovery of a 4 kpc molecular gas lane in the Cygnus A host galaxy, using Atacama Large Millimeter/submillimeter Array CO 2-1 observations. The gas lane is oriented roughly perpendicular to the projected radio jet axis. The CO emission generally follows the clumpy dust lanes seen in Hubble Space Telescope I-band images. The total molecular gas mass is 30 × 10⁸M_⊙ for Milky Way-type clouds, and 3.6 × 10⁸M_⊙ for starburst conditions. There is a velocity change from the northern to southern CO peaks of about ±175 km s^–1, and an apparently smooth velocity gradient between the peaks, although the emission in the central region is weak. In the inner ∼0.″5 projected distance from the radio core, comparison of the CO velocities to those observed for H₂ 2.1218 μm emission shows higher velocities for the vibrationally excited warm molecular gas than the cooler CO 2-1 line emitting gas at similar projected radii. A possible explanation for these different projected velocities at a given radius is that the cooler CO gas is distributed in a clumpy ring at radius ∼1.″5-2″, while the warm H₂ 2.12 μm emitting gas is interior to this ring. Of course, the current data cannot rule out a clumpy, amorphous molecular gas distribution linearly distributed perpendicular to the radio jet axis. We consider surface brightness properties on scales down to ∼265 pc, and discuss the Cygnus A results in the context of other radio galaxies with CO emission.