Plasma and Warm Dust in the Collisional Ring Galaxy VII ZW 466 from VLA and ISO Observations

December 1999 • 1999ApJ...527..143A

Authors • Appleton, P. N. • Charmandaris, V. • Horellou, C. • Mirabel, I. F. • Ghigo, F. • Higdon, J. L. • Lord, S.

Abstract • We present the first mid-infrared (mid-IR) (5-15 μm) and radio continuum (λ=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 λ=9.6 μm) 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 λ=15.0 μm 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.

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Phil Appleton

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