| |
 |
| Paper: |
Gradients in the Outer Halo |
| Volume: |
92, Formation of the Galactic Halo. . . . Inside and Out |
| Page: |
499 |
| Authors: |
van den Bergh, Sidney |
| Abstract: |
The Searle-Zinn (1978) scenario for the formation of the Galactic halo was mainly motivated by the unexpected discovery of Searle (1977) that globular clusters in the outer halo do not exhibit a radial metallicity gradient. However, a plot of globular cluster half-light radius r_h versus Galactocentric distance R (see Fig. 1, bottom) does show a gradient (van den Bergh 1995). This suggests that the radii of clusters may be determined by global factors, whereas the metallicity of clusters might have been influenced more strongly by local factors. Surprisingly, Fig. 1 (top) shows that the half-light radii of globular clusters correlate more strongly with perigalactic distance P than they do with present Galactocentric distance R. The reason for this difference is not known. For globulars with R > 20 kpc, the rank-correlation coefficient between R and r_h is rho = +0.61 +/- 0.18. However, a much stronger correlation rho = +0.84 +/- 0.18 is found between r_h and the perigalactic distance P. It is presently not clear how the correlation between R and r_h , and the even stronger correlation between P and r_h , is to be reconciled with the Searle- Zinn scenario. Fig. 1 also shows that globular clusters in retrograde orbits are smaller than those that have direct orbits. |
|
|
|
|
|
