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| Paper: |
Star Formation and the Color—Age Sequence in the Inner Resonance Ring of the Galaxy NGC3081 |
| Volume: |
316, Order and Chaos in Stellar and Planetary Systems |
| Page: |
276 |
| Authors: |
Freeman, T.; Byrd, G.; Buta, R. |
| Abstract: |
We complement Buta, Byrd, & Freeman’s (2004) HST observations of NGC3081’s inner r ring using an analytical approach and n-body simulations of this galaxy. We find: A long-lived (5 × 109 yr) gas cloud ring of periodic orbits forms under a rotating bar perturbation. The misalignment of the major axis of the nuclear ring (nr) from 90° to the bar can be created by dissipation in the gas clouds. The perturbation creates pointy ends and transverse crowding in the r ring at the major axis, both favorable to stellar association formation. Ring elongation increases with perturbation strength. The azimuthal surface mass density variation and the fractional long wavelength light variation give a stellar disk surface density of roughly 50 Solar masses/pc2 at the r ring, 1/5 that of a 100% disk sufficient to explain the rotation curve, i.e., the galaxy is halo dominated. NGC3081's disk and the bar pattern turn counter clockwise (CCW) on the sky with a aster orbital angular rate than the pattern inside the ring edge. Thus the r ring’s CCW displacement between the m = 2 Fourier I and B peaks along the r ring from the bar inside co-rotation (CR) must result from the time delay before “lighting up” in the blue by stellar associations formed near the bar. Further observations are needed to verify the NGC3081 “formation to light up” delay. The outer edge of the ring at the bar orbits with the pattern speed, supported by the superposition of the I and B peaks and the wide range of association ages there. The ring edge is smaller than CR. Near the theoretically expected halo value, our simulations form gas cloud “associations” near the ends of the bar as observed. Grant support NASA/STScI GO 8707 and NSF AST-0206177 (TF, GB). |
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