| 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 |
| URL |
http://adsabs.harvard.edu/abs/2009AAS...21344412S |
| 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. |