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The Ringed X-Galaxy NGC 7020

Published online by Cambridge University Press:  12 April 2016

Ronald Buta
Ronald Buta*
Affiliation:
Department of Physics and Astronomy, University of Alabama, U.S.A.

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The southern S0+ galaxy NGC 7020 presents an unusual morphology: it includes a very regular outer ring which is completely detached and which envelops an inner ring/lens zone with a hexagon surrounding an X shape (Figures 1a and 1b). The outer ring has a high contrast compared to those usually observed in barred galaxies, yet NGC 7020 is not obviously barred. The morphology of this galaxy poses an interesting puzzle in that the hexagonal/X zone is not a typical type of feature to find in the interior of such a regular ring. Instead, the zone bears a striking resemblance to the edge-on galaxy IC 4767, recently studied by Whitmore and Bell (1988 = WB88) and dubbed by them as the “X-galaxy” because its inner regions appear to be crossed by two distinct enhancements lined at ±22° with respect to the major axis. The observation of a similar phenomenon in NGC 7020 is interesting because of the suggestion by WB88 that “X” structures could be related to accretion of matter associated with a merger or tidal encounter between an SO and a small satellite galaxy. If this interpretation is correct for NGC 7020, then it has important implications for the nature of the outer ring. An alternative interpretation is that the inner hexagonal/X zone is a region where resonant periodic orbits in a weak bi-symmetric potential perturbation are influencing the morphology more strongly than might be expected. In this paper, I give a brief summary of a more extensive paper (Buta 1990c = B90c) and a few other details concerning this interesting galaxy.

Type
III. Observations of Related Objects
Information
International Astronomical Union Colloquium , Volume 124: Paired and Interacting Galaxies , 1990 , pp. 189 - 193
Copyright
Copyright © NASA 1990

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