The Physical Properties of Cosmological Halos: Environmental EffectsJuhan Kim & Changbom ParkKorea Institute for Advanced Study

History of Universe

Large-scale StructuresDubinski 2003

What is dark matter halo?Evrard and White et al. (1993)Not spherical!ROSAT

what we dont seeDark Matter Halo much larger than the galaxy itself!How do we know this?

From the circular velocities of stars and molecular hydrogen in the disk of spirals (recall flat rotation curves) and from the highly non-circular stellar orbits in elliptical galaxies.Key propertySame velocity spread of particlesindependent of position within the halo and density of material 1 / r2

Basic picture of the formation processbaryonsdark matterbaryonsr, THydrodynamicsGravityChemical reactionsCooling/Star formation

A New Parallel N-body CodeC2AP (Cosmological Code for Astrophysical Problems)An improved version of the former code, GOTPM (2-3 times faster)Supporting arbitrary number of CPUs (but not for serial)using z-directional domain slabs with variable widths equal load of memory (& equal CPU time is possible.) & maximizing the usage of memory spaceUsing FFTW (ver. 2) for full parallel Fast-Fourier-Transform (FFT)Supporting OpenMP ( but not in the FFT)

Force Measuring (hybrid method)r d dk jk j forceFFTPM force (measuring global force)Tree force (correcting local force)

Oct-Sibling Tree (OST)Oct Tree: spatially decomposes particles into hierarchical particle groupsSibling Tree: rather than using eight daughter pointers, it uses one sibling pointer

Dynamic Domain DecompositionWhen calculating FFTExcept for the FFT

Parallel PerformanceFor 40963 particle simulation, it will take about one hour with 512 IBMSP3 CPUs.

Effect of Gravitational EvolutionHigh density region collapse forming galactic & cluster halosLow density region expand forming cosmic voids

Density Evolution from Quantum FluctuationsA few hundreds galaxiesNearly smooth homogeneous & isotropic background

PSB HalosGroup finding from particle distributionPSB (Physically Self-Bound) method (Kim & Park 2006)Halo-halo boundary ConstraintsTotal EnergyTidal Radiussubhalo in haloAssumed to be individual haloSubhalo ~ galaxyHalo information galaxy informationMock galaxy redshift surveyWhat we can get from simulation are..xcorrelationGenus statisticsHalo massfunction, shape, rotation angle, spin parametersWe can compare the simulation results with observations directly.PSB Halos

Halo Mass FunctionSheth & Tormen: the best fitting MF for FoF groups proved in others simulation resultsFoF: only FoF group are counted.Well fitted by the S-T at z=0Well fitted by the P-S at z=7Different from other researches. The reason of difference of FoF MF from others Different simulation resolution in mass & forcePSB: subhalos are counted as individual halos.Difference of MF btw. FoF & PSB At z=7, same MFAt z=0, significantly different at high mass tail

Z=0Z=7PSBFoF

Halo Shape Fittinga=b=c : spherea=b>c : oblate spheroid (disk-shaped)a>b=c : prolate spheroid (cigar-shaped)a>b>c : scalene (triaxial)oblateprolateShape Tensor : Sij = S xi xj3 eigen vectors : directional cosine of axes3 eigen values : two ratios ratios of radii

Definition of Local DensityUsing spline kernel to measure local density with a variable smoothing length ( = distance to 20th neighboring seed halo)How to define density seeds?Observation: L* (-21

SDSS & Simulation density histogramM

Halo ShapeOblate ProlatedensemassiveHalos In denser environment more oblateMore massive halos more prolateRoundness: qxs = bc/a2halo Triaxiality (Warren et al. (1992); Bailin & Steinmetz (2004):0 < T < 1/3 : Oblate pancake like1/3 < T < 2/3 : scalene 2/3 < T < 1 : Prolate needle like

Spin DistributionSpin :

Well fitted by the Gamma distribution rather than log-normal

No significant change of k (~ 3.6)In denser region smaller b halo rotate fasterMassive halo higher b rotate slower

Relation btw. Rotation & Shape AxesRotation & major axes orthogonalRotation & intermediate axes no relationRotation & minor axes parallelNo obvious environmental effect on these relations

A new version of GOTPMFaster & less usage of memory spaceHalos tend to be more prolate.but in dense region they tend to be more oblate.more massive halos tend to be more prolatespin distribution well described by the Gamma distributionIn denser region, halos rotate faster.More massive halos rotate slower.Halo rotation axis ~ halo minor axis