Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.8399n&link_type=abstract
HST Proposal ID #8399
Astronomy and Astrophysics
Astrophysics
Hst Proposal Id #8399 Distant Galaxies
Scientific paper
NGC 4650A is a classic example of a polar ring galaxy in which an outer disk orbits in approximately the polar plane of an inner, high surface brightness S0 galaxy. Polar ring {PR} galaxies are astrophysically important as highly visible examples of the e ffects of interactions and/or gas capture in galaxy evolution. Because they have two planes of rotation, they also provide unique opportunities to explore the extent and structures of `dark matter halos'. In this Hubble Heritage project we will provide a superb color image of NGC4650A obtained through a combination of observations in the blue, visual, and near infrared WFPC2 bandpasses. The resoltuion provided by WFPC2 will provide the first close-up view of the mysterious inner S0 disk system, as well as allowing us to explore the structural details of the larger polar disk. In this object we will search for evidence of effects of gravitational instabilities within the polar disk, ranging in spatial scale from dark cloud co mplexes to spiral arms, as a m eans to assess the importance of self-gravity within this subsystem. A dynamical analysis by Sackett and Sparke {1990, ApJ, 361, 408} as well as later imaging and kinematic investigations {Arnaboldi et al. 1997, AJ, 113, 585} suggest that the polar ring d isk could be more massive than suggested by HI and optical observations. This information will lead to a better understanding of the degree to which the dark matter is dominant far above the midplane of the central galaxy in NGC4650A. Our program is also designed to explore characteristics of small scale features within this unusual galaxy. For example, since PRs may result form mergers or interactions between galaxies, we need to be alert to the presence of aging super star clusters {or younger globular clusters} as well as the possibility of nuclear region anomalies.
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