The Formation of the Milky Way

largely a discussion topic...

Based on the properties of the Milky Way, two competing scenarios have been put forth over the years to describe the formation of the Galaxy:
 

Monolithic Collapse
(Eggen, Lynden-Bell, and Sandage, 1960s)
Hierarchical Accretion
(Searle and Zinn late 1970s)
Idea: 
Giant, massive cloud of gas (~100 kpc across) collapses down to form the Galaxy.
 Idea: 
Lots of small "proto-galactic lumps" merge together to form a bigger galaxy.

Questions:

Keep these ideas in mind as we begin to study other galaxies...