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T. Freeman (Bevill State Brewer Campus, Fayette, AL), G. Byrd, R. Buta (Univ. of Alabama, Tuscaloosa)
We complement our HST observations of the inner resonance ring of the galaxy NGC3081 (Buta, Byrd, & Freeman 2003) with a a theoretical perturbative analytical approach and n-body simulations. The ring shape gives the potential perturbation strength of the bar and the surface mass density variation around the ring. Combining with the observed two-fold and circularly symmetric intensities gives a disk surface density of ~ 46MSolar Masses pc-2 near the inner ring, a small fraction of that necessary to fully explain the rotation curve (i.e. the galaxy is halo dominated). We explain enhanced star formation near the ring’s major axis via strong transverse crowding. Radial crowding near the minor axis is less effective. As expected, the exterior edge of the ring has no displacement between the colors and also a wide range of association ages. This edge is at radius 38.5" < co-rotation 54" as expected. At radii < 38.5", CCW angular color displacement increases until the interior edge of the ring. We find a CCW angular color sequence with increasing age of associations formed near the ends of the bar near the interior edge of the ring. The sequence is thus I, V, B with increasing age. Both orbit and pattern speed are thus CCW on the sky. Sense of disk rotation can thus be determined for galaxies with less data or favorable orientation than NGC3081. The ring lasts several billion years in our simulations depending on the galaxy halo. With a sufficiently low halo (but halo-dominated) our simulations form gas cloud ``associations" near the ends of the bar, consistent with observations and theory. Too low a halo results in a chaotic non-ring disk. Grant support: NASA/STScI GO 8707 and NSF AST-0206177.
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The author(s) of this abstract have provided an email address for comments about the abstract: tfreeman@bscc.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.