Merging, Mixing, and Disk Destruction

 

Violent relaxation during a major merger destroys the disks and rapidly produces a r1/4-like profile (Barnes 1988, 1992; Hernquist 1992, 1993) in the remnant. 

However, this mixing is far from complete (Barnes 1992) and does not completely erase population gradients in the progenitors (White 1980; Mihos & Hernquist 1994). 


For pure stellar-dynamical disk mergers, gradients are reduced by ~ half, and retain their original form (i.e. exponential vs power law). Mixing is reduced in more concentrated components (e.g., White 1980), so that bulges should retain more of their original gradients.


(from Barnes 1992)

 

The remnants also retain a large degree of kinematic memory about both the interaction and of the progenitor galaxies. Transfer of angular momentum from the orbit to internal spin produces remnants which rotate at large radius:


(from Hernquist 1992)


How well can disks survive? "Disky" vs "disks"

     
  • 1:1 mergers destroy the disk, leave boxy anisotropic remnants with little or no rotation (Barnes 1992, Hernquist 1992, Naab etal 1999).
  • 3:1 mergers are more complicated. They show diskier isophotes

    • (from Naab, Burkert, and Hernquist 1999)

    and they retain significant rotation   . 

         

(from Bendo & Barnes 2001)

However, as structural entities, the disks have been destroyed. These remnants largely retain r 1/4 profiles indicative of the violent merger (Naab etal 1999; Bendo & Barnes 2001).


From Naab (2000) simulations of B:D=1/3 mergers:
Mass Ratio
Sersic "n"
1:1
0.2 - 0.3
2:1
0.2 - 0.35
3:1
0.3 - 0.4
4:1
0.3 - 0.5
  • n=0.25: de Vaucouleur law
  • n=1:      exponential disk