Speculation and Future Goals

Critical question: Do mergers create/destroy/affect the central parameter relationships?

In particular, what is the fate of objects like NGC 3921 and NGC 7252?



Option 1: They'll fade photometrically onto the normal relationship

• need about 2 - 2.5 magnitudes of fading
• addition of low res spectroscopy to construct population synthesis models

Option 2: They'll evolve dynamically onto the normal relationship

• binary black hole slingshot mechanism (eg Quinlan & Hernquist 1997, Milosavljevic & Merrit 2001)
• but stellar dynamics are unclear
• high res spectroscopy to look at nuclear dynamics and presence of black holes

Option 3: They'll stay wierd and this hurts the "merger hypothesis"


Option 4: They'll stay wierd. So what?

• Today's merger remnants merged at z ~ 0.
• Today's normal ellipticals (under the merger hypothesis) merged at z >= ~ 1
• Progenitors were likely quite different:
  • Higher gas fractions?
  • Closer to star formation "thresholds" (Quirk 1972, Kennicutt 1989)?

    z=0	z=2
    from Kauffmann 1996

    
    
  • Different structurally (surface density, D:B ratio, etc)?
  
  
• Balance between inflow/nuclear starbursts vs disk-wide star formation can differ widely depending on the structure of the merging galaxies.

Evolution vs "Prevolution" - rather than "trying to fix" NGC 3921 and NGC 7252, perhaps they are the future of elliptical galaxies...