A 4~Kpc Molecular Gas Lane in Cygnus A

C. L. Carilli, R. A. Perley, D. A. Perley, V. Dhawan, R. Decarli, A. Evans, K. Nyland

Submitted on 2 September 2022


We present the discovery of a 4 kpc molecular gas lane in the Cygnus A host galaxy, using ALMA 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 HST I-band images. The total molecular gas mass is 30×108 M for Milky Way type clouds, and 3.6×108 M for starburst conditions. There is a velocity change from the northern to southern CO peaks of about ±175~km~s1, 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" to 2", while the warm H2 2.12μm 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.


Comment: 5 Figures, 23 pages, 2 tables, accepted for publication in the ApJ

Subject: Astrophysics - Astrophysics of Galaxies