Mergers and the Formation of Elliptical Galaxies 

Galaxy formation through mergers: structure forms hierarchically observational record of nearby mergers (Really talking about ~ L*-ish E's, not so much luminous cluster E's or dE's)

NGC 7252, from Hibbard etal 1994

Simulations let us watch this transformation:

At least some nearby ellipticals show evidence for a merger origin: diffuse tidal debris cold gas rising v/sigma kinematically decoupled cores bimodal GC distributions Open Questions: What fraction of ellipticals had this sort of merger origin? When did these mergers happen? What did the progenitors look like?

Centaurus A, from Schminovich etal 1996

A classic objection to making E's through mergers (of spirals) was the central density problem: spirals have lower central densities than ellipticals, which is preserved upon merging (eg Hernquist 1992). I do not think you can make rocks by merging clouds -- Gunn (1977) Possible Solutions: Pre-existing bulges in the merging progenitors (Hernquist 1993) Central starbursts -- but would this happen seamlessly?	from Carollo (1999)
Mihos and Hernquist (1994)	Hibbard and Yun (1997)

But the physics is too complicated to model -- time to log off the computer and go to the data...

NGC 6240, from van der Marel etal, in prep