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Register a new userPlasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations
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Added by
Vassilis Charmandaris
Publication date
1999
fields
Physics
and research's language is
English
Authors
P.N. Appleton
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We present the first mid-infrared (Mid-IR) ($lambda5-15mu$m) and radio continuum ($lambdalambda$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 and the NRAO Very Large Array. A search was also made for CO line emission in two of the galaxies with the Onsala 20m 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 which 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 $lambda9.6mu$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 observations at $lambda15.0mu$m show possible emission inside the ring, with little emission directly associated with the ion{H}{2} 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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Collisional ring galaxies probably result from a head-on collision between a compact companion galaxy and a gas-rich disk system. We present a review of the discovery of warm dust in five collisional rings observed by ISO which range in total Far-IR luminosity from 10$^{10}$~ $<$ ~L$_{FIR}$ ~$<$ ~10$^{11}$ L$odot$. The results show that in most cases, the mid-IR (MIR) flux is often a significant fraction of the total energy budget of star formation activity in these galaxies (at least 10% even in the least powerful cases). We argue that the MIR emission, when combined with optical and radio observations, allows us to build a more complete picture of activity in these collisional systems. Although not as extreme as ULIRGs, these collisional systems provide low-redshift examples of the early effects of galaxy collisions on the ISM and may be relevant to the collisional assembly of galaxy disk components at high redshift.
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