Groups of galaxies - a few to a few dozen galaxies - with mass ~10 trillion solar masses
Contain most of the mass, galaxies and baryons of the universe
How do they form, evolve, and die?
How do simulations and observations compare?
PKDGRAV -- Particle gravity tree-code -- Spatially and temporally adaptive
Joachim Stadel & Tom Quinn
Initial Conditions - "Standard" Big Bang Model (complex physics)---> redshift ~ 70 (gravity dominates)
Evolve a cosmological cube of 80 million dark matter particles to present day
~ 100 galaxy groups
Galaxies (gas rich / spirals) infall towards a local overdensity
Dense group is formed
Galaxy merging, tidal stripping, infalling gas --> substructure erased
Galaxies transformed into ellipticals
Gas heated and diffused into same distribution and temperature as dark matter
End State: Merger remnant - giant elliptical galaxy within a diffuse halo of dark matter and X-ray emitting hot gas
Identification: Is it a ``real'' group?
Expect: a common dark matter halo - traced by diffuse X-ray halo
Many groups have no X-ray halos --- Is there no intragroup gas or is the gravitational potential too shallow?
``2-D'' observations --> many spurious superpositions,
Group X-ray halos are faint, and maybe too cool to have been detected
But - observations are difficult
Simulating the mass is easy, but comparison with observations is not
Need to model observables
Model the gas: AMR, SPH, semi-analytic
Can't resolve stars
Simulated observations in X-ray and Optical
Correlate mass with observables
Compare real mass with simulated mass
Test/improve models of group evolution
Why have compact groups not yet merged?
Where does the X-ray gas come from?
Test/improve Big Bang models
What to do with X terabytes of data
More simulation
info:
www.nbody.net