Evolution of Merging Galaxies

 
Dynamical modeling (Mihos & Hernquist 1994, 1996)
 
  • Gravity: Lagrangian N-body dynamics: disk, bulge, dark halo
    • Initial conditions based on present-day disk galaxies
  • Hydrodynamics: Lagrangian Smooth Particle Hydrodynamics
    • exponential disk; Mgas = 10% Mdisk
  • Star formation: simple density dependence
    • Schmidt law or gravitational collapse:

 
 
The self-gravity of the stellar disks can lead to strong non-axisymmetric structures (bars, spiral arms) in the disk. 

Gas is "swept up" along these features, experiences strong gravitational torques, and loses angular momentum, flowing in towards the nucleus.

 
 
This inflow, in turn, is very effective at driving strong bursts of star formation in the merging galaxies, and depleting the gas.

Detailed response is very sensitive to the structure of the galaxies, which can amplify or supress the instabilities which drive inflow.

Supernovae and starburst winds may feed a halo of hot X-ray emitting gas.
 

 
 
Do we see examples of this in the local universe? Yes!

Ultraluminous infrared galaxies 

    (Lfir ~ 1011 - 1012 Lsun)
  • dust enshrouded
  • close mergers
  • nuclear gas concentrations and starbursts
  • many have X-ray halos
Ellipticals in formation?
from Hibbard and Yun 1997
 

And we also see the starburst galaxies forming X-ray halos: