Stuart D. Ryder, PASA, 14 (2), in press.
Next Section: Acknowledgments Title/Abstract Page: Fundamental Relationships in Galactic Previous Section: A Relationship Between Stellar | Contents Page: Volume 14, Number 2 |
Conclusions
We have demonstrated that the following three (azimuthally-averaged) observational parameters are correlated at each radius in the disks of nearby spiral galaxies:
- - the surface density of old stars;
- - the recent formation rate of massive stars per unit area; and
- - the mean gas-phase abundance of oxygen in HII regions, the current sites of star formation,
and
where is the HI mass per unit area of the star-forming disk. As a consequence of these new observational relationships, and our attempts to interpret them using galactic evolution models, two important results have emerged:
- The return of oxygen to the ISM by dying low-mass stars late in the galaxy's lifetime can make a significant contribution to the gas-phase oxygen abundance at late epochs.
- The ``classical'' Schmidt Law for star formation cannot simultaneously satisfy both the () and the () relationships; some dependence on the total mass surface density (or some other quantity that scales with it) is also required.
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