* Astronomy

Title: NGC922 - A new drop-through ring galaxy
Authors: O. I. Wong, G. R. Meurer, K. Bekki, D. J. Hanish, R. C. Kennicutt, J. Bland-Hawthorn, E. V. Ryan-Weber, B. Koribalski, V. A. Kilborn, M. E. Putman, J. S. Heiner, R. L. Webster, R. J. Allen, M. A. Dopita, M. T. Doyle, M. J. Drinkwater, H. C. Ferguson, K. C. Freeman, T. M. Heckman, C. Hoopes, P. M. Knezek, M. J. Meyer, M. S. Oey, M. Seibert, R. C. Smith, L. Staveley-Smith, D. Thilker, J. Werk, M. A. Zwaan

Researchers have found the peculiar galaxy NGC922 to be a new drop-through ring galaxy using multi-wavelength (UV-radio) imaging and spectroscopic observations. Its `C'-shaped morphology and tidal plume indicate a recent strong interaction with its companion which was identified with these observations. Using numerical simulations they demonstrate that the main properties of the system can be generated by a high-speed off-axis drop-through collision of a small galaxy with a larger disk system, thus making NGC922 one of the nearest known collisional ring galaxies.
While these systems are rare in the local Universe, recent deep HST images suggest they were more common in the early Universe.



The greyscale optical image (top) is a deep image from digitally stacked plates of NGC922 (bottom-left) and S2 (top-right). The height of the greyscale image is about 4'. The enlarged images are SINGG-SUNGG composite images of NGC922 and S2 where red represents Ha, green represents R-band and blue represents FUV. A diffuse plume of stars on the northwestern side of NGC922 can be seen in the R-band to be extending towards the companion.

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