Plasma and warm dust in the collisional ring galaxy VII Zw 466 from VLA and ISO observations

We present the first mid-infrared (mid-IR) (5-15 mu m) and radio continuum (lambda = 20, 6, and 3.6 cm) observations of the star-forming collisional ring galaxy VII Zw 466 and its host group made with the Infrared Space Observatory (ISO) and the NRAO Very Large Array. A search was also made for CO line emission in two of the galaxies with the Onsala 20 m radio telescope, and upper limits were placed on the mass of molecular gas in those galaxies. The ring galaxy is believed to owe its morphology to a slightly off-center collision between an "intruder" galaxy and a disk. An off-center collision is predicted to generate a radially expanding density wave in the disk that should show large azimuthal variations in overdensity and have observational consequences. The radio continuum emission shows the largest asymmetry, exhibiting a crescent-shaped distribution consistent with either the trapping of cosmic-ray particles in the target disk, or an enhanced supernova rate in the compressed region. On the other hand, the ISO observations (especially those made at lambda = 9.6 mu m) show a more scattered distribution, with emission centers associated with powerful star formation sites distributed more uniformly around the ring. Low signal-to-noise ratio observations at lambda = 15.0 mu m show possible emission inside the ring, with little emission directly associated with the H II regions. The observations emphasize the complex relationship between the generation of radio emission and the development of star formation even in relatively simple and well-understood collisional scenarios.