The Polar Rings Around NGC 5122 And UGC 7576: Superthin Quiescent Low-surface-brightness Disks

Type Conference Paper
Names Linda S. Sparke, G. van Moorsel, A. L. Cox
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #213, #444.12
Volume 41
Pages 328
Date January 1, 2009
Short Title The Polar Rings Around NGC 5122 And UGC 7576
Library Catalog NASA ADS
Abstract NGC 5122 and UGC 7576 are small lenticular galaxies encircled by a polar ring or disk of gas and stars. Our VLA 21cm maps show a few billion solar masses of neutral hydrogen gas in each ring, extending at least 25kpc from the gas-poor central galaxy. NGC 5122 has at least two gas-rich companions. Both rings are seen nearly edge-on; in starlight they are 'superthin', with axial ratios of at least 10:1. Although extremely gas-rich, neither ring shows knots of young stars. Our HI data cubes show that the rings are not radially-thin annuli, but broad disks with central holes. The ring around NGC 5122 lies almost exactly along the minor axis of the central stellar body, but that around UGC 7576 is tilted about 15 degrees from polar, and is also slightly banana-shaped. The tilted gas orbits in UGC 7576 must precess in the gravitational field of the oblate central galaxy; inner orbits tend to precess faster, twisting the ring. The baryonic content of the ring is comparable to that of the central stellar body. Thus the tilted ring may be stabilized by its self-gravity, so that it precesses as a unit and can remain untwisted. We thank the National Science Foundation for grant support.
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