John Dubinski

The Structure of cold dark matter halos

The density profiles and shapes of dark halos are studied using the results of N-body simulations of the gravitational collapse of density peaks. The simulations use from 3×10 4 to 3×10 5 particles, which allow density profiles and shapes to be well resolved. The core radius of a typical dark halo is found to be no greater than the softening radius, e=1.4 kpc. The density profiles can be fitted with an analytical model with an effective power law which varies between −1 in the center to −4 at large radii. The dark halos have circular velocity curves which behave like the circular velocity contribution of the dark component of spiral galaxies inferred from rotation curve decompositions.

The Origin of the Brightest Cluster Galaxies

Most clusters and groups of galaxies contain a giant elliptical galaxy in their centers that far outshines and outweighs normal ellipticals. The origin of these brightest cluster galaxies is intimately related to the collapse and formation of the cluster. Using an N-body simulation of a cluster of galaxies in a hierarchical cosmological model, we show that galaxy merging naturally produces a massive central galaxy with surface brightness and velocity dispersion profiles similar to those of observed BCGs. To enhance the resolution of the simulation, 100 dark halos at z = 2 are replaced with self-consistent disk + bulge + halo galaxy models following a Tully-Fisher relation using 100,000 particles for the 20 largest galaxies and 10,000 particles for the remaining ones. This technique allows us to analyze the stellar and dark-matter components independently. The central galaxy forms through the merger of several massive galaxies along a filament early in the clusters history. Galactic cannibalism of smaller galaxies through dynamical friction over a Hubble time only accounts for a small fraction of the accreted mass. The galaxy is a flattened, triaxial object whose long axis aligns with the primordial filament and the long axis of the cluster galaxy distribution, agreeing with observed trends for galaxy cluster alignment.

THE EFFECT OF DISSIPATION ON THE SHAPES OF DARK HALOS

The dissipative infall of gas during the formation of a galaxy modifies the density profile and shape of the dark halo. Gas dissipates energy radiatively and sinks to the center of the dark halo forming the luminous part of a galaxy. The resulting central density enhancement can alter the halos orbital distribution. We simulate dissipative infall inside of an initially triaxial N-body dark halo by slowly growing a potential in the center of the particle distribution. The dark halo transforms from a prolate-triaxial halo (

Dynamical Blueprints for Galaxies

T \sim 0.8

A parallel tree code

) to an oblate-triaxial halo (

Constraining Dark Halo Potentials with Tidal Tails

T \sim 0.5

Using tidal tails to probe dark matter halos

) while approximately preserving the flattening (

DEEP CCD SURFACE PHOTOMETRY OF GALAXY CLUSTERS. II. SEARCHING FOR INTRACLUSTER STARLIGHT IN NON-cD CLUSTERS

c/a \sim 0.5

Turbulence in Molecular Clouds

). The main implication is that dark halos are rounder and more oblate than previous predictions of purely collisionless simulations with the new constraint that

The Horizon Run N-body Simulation: Baryon Acoustic Oscillations and Topology of Large Scale Structure of the Universe

b/a \gapp 0.7