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| Paper: |
Constraints on Theories of Galaxy Formation |
| Volume: |
92, Formation of the Galactic Halo. . . . Inside and Out |
| Page: |
403 |
| Authors: |
Wyse, Rosemary F. G. |
| Abstract: |
The properties of the stellar populations of the Galactic halo contain important information as to the location and duration of early star formation. The element ratios of halo stars are consistent with a massive-star IMF that is invariant, and with enrichment by Type II supernovae only. Thus star formation in halo star-forming regions was only of short duration, as predicted if the halo star-forming regions have shallow potential wells. A range of ages in the stellar halo requires a range of times at which star formation is initiated in different regions. Perhaps 10% of local halo stars are younger than the dominant old population; these younger stars are also predominantly more metal-rich than the dominant halo field population. The present-day retinue of gas-poor satellite galaxies to the Milky Way contains a predominantly metal-rich, intermediate-age population, and accretion of a few galaxies such as these could account for the observed tracer population of younger halo stars. Merging of more massive, more dense satellites is constrained by the properties of the Galactic thick disk, which is old, to have occurred only a long time ago. |
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