KITP: The Big Questions

Today we step back and Hans runs The Big Questions past us.

It is always good to think about the Big Picture.

The Big Questions

1. Most likely scenario for cluster formation:
   • a) compressed/triggered initial conditions: cloud collisions or intersecting shells, or
   • b) did globular clusters form as nuclei in dwarf galaxies that got accreted by our MW (dE,N hypothesis), or
   • c) scaled-up version of open cluster formation in mol. clouds? (Pudritz papers, Krumholz talk); the role of high pressure?

   
   
   

2. Relation of halo stars and globular cluster destruction ... (are Pop II stars dissolved globular clusters or something else?) How much of their original mass do globular clusters retain?
3. Why are there no globular clusters with metallicity [Fe/H] = -3 but halo stars with [Fe/H] = -5. Top-heavy IMF for lower [Fe/H]? Why are globular cluster populations so extremely well mixed?
4. Did globular clusters have an ordinary IMF (ratio low/high m) like open clusters today? IMF of multiple populations the same? How did stellar dynamics and cluster evolution change the IMF?
5. Did the binary properties at birth differ in globular clusters from those of current open clusters and if so why? mass-dep.? What are the observed binary properties of Pop II halo stars?
6. How to explain the origin of the multiple stellar populations? (Piotto, d'Antona, etc), is high-He pop. due to AGB enrichment? How much gas and dust has been shed and lost causing expansion?
7. Are young high-z globular clusters sites for GRB? observable? Is there enough time for O-stars to collide in protoglobulars? Are runaway collisions possible in a mass-segregated cluster?
8. How many stellar mass BHs should a typical GC contain today? what about an intermediate mass BH in the very dense center?

   
   
   

9. Is 30 Doradus or Westerlund 1 a protoglobular cluster? mass? core radius, surface brightness profile, binary fraction?

   
   
   

10. Globular cluster systems, specific frequency (number/lum.); what are the most important trends with their host galaxies?

Hans Zinnecker Feb. 10, 2009, KITP, Santa Barbara

We don't get to go home until we have answered these.