1. Racah Institute of physics, Hebrew University (Jerusalem, Israel)
Structure Formation in the Universe: Simulating Our Local Cosmic Neighborhood Yehuda Hoffman (HU) Formation of Local Universe University of kentucky (Apr 2008)
Title:
Structure Formation in the Universe: SImulating Our Local Cosmic Neighborhood
The early universe was homogenous and isotropic down to small fluctuations of the order of 1.e-5 or smaller. Out of these primordial random perturbation field structure has evolved by means of gravitational instability. Gravity drives dark matter to collapse and virialize in bound clumps, known as dark matter halos, which further cluster to form the cosmic web made of clusters, filaments, sheets and voids. The baryonic matter, in the form of gas, responds to the gravitational pull of the dark matter and settles at the cores of the dark matter halos where it cools and forms stars, thereby forming the visible galaxies. Using the algorithm of constrained realizations of Gaussian random fields we simulate the formation of the local universe, including the Local Group that contain the Milky Way and the Andromeda galaxies.
Yehuda Hoffman
Racah Institute of physics, Hebrew University (Jerusalem, Israel)
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

2. Cosmological Time Line
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)
Yehuda Hoffman (HU) Formation of Local Universe University of kentucky (Apr 2008)

3. Cosmic Microwave background: Temperature Fluctuations
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

4. Detection of dark matter
Gravitational Lensing
Galaxy cluster Abell 1689
Distance 2 million Ly
Gravitational lensing predicted by Einstein’s general relativity
The gravitational mass exceeds the mass seen in light & X-ray
=====> DARK MATTER
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

5. Detection of dark energy
Supernovae Type Ia
Standard candles
Observed magnitude vs redshift
High redshift SN are fainter than expected in “standard” cosmologies
Universe is currently accelerating
=====> DARK ENERGY
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

6. Content of the Universe
Angular Power Spectrum
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

7. What have we learned from WMAP?
ΛCDM standard model
The Universe is flat - Euclidian geometry
The mass-energy budget of the Universe:
4.5% ordinary matter (baryons)
23% non-baryonic unknown dark matter
Dark matter is cold
( )% cosmological constant (Λ)? dark energy?
All structure emerged from quantum fluctuations of the vacuum in the very early universe (≈10-30s after the Big Bang)
Cocktail party remark:
Everything has formed from nothing
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

8. τplanck=(Gh/c5)1/2≈10-44s Structure Formation
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

9. Structure & Galaxy Formation
Dark Matter
dynamics: gravity - Newtonian, non-linear, non- dissipative
Baryons
dynamics: gravity, hydrodynamics, radiation
physical processes: star formation, stellar feedback, cooling & heating ... (sub-grid)
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

10. Initial Conditions
Primordial perturbations constitute a Gaussian random field
The power spectrum (shape & normalization) is determined from the CMB: (Δ T / T) ≈ 10-5
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

11. Prevailing idea: dark matter talks & baryons listen
Dark matter clusters and forms bound objects (called DM halos) - GRAVITATIONAL INSTABILITY
Baryons follows the gravitational pull of the dark matter
Baryons cools radiatively, sinks to the bottom of the DM halos & form stars - GALAXY FORMATION
Complex non-linear gravitational, hydrodynamical, radiative, star formation & stellar evolution processes determine the structural, dynamical, stellar & chemical properties of galaxies
Massive numerical simulations are the main tool used to study these complex phenomena!
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

12. N-body simulations: gravity only Distribution of DM halos
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

13. Conditional Luminosity Function:
Φ(L|M)dL is the average # of galaxies in the range of L±dL/2 residing in a DM halo of mass M
(van de Bosch et al 2007)
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

14. Millennium Simulation: N-body + Semi-analytical ModelingDM
Populating DM with galaxies:
Identify DM halos
Construct the merging history of each halo
Apply simplified analytical recipes to model galaxy formation for each halo at any given time
Form galaxies in the DM halos
Millenium:
Introduction: The Millennium Simulation
The Millennium Run used more than 10 billion particles to trace the evolution of the matter distribution in a cubic region of the Universe over 2 billion light-years on a side. It kept busy the principal supercomputer at the Max Planck Society's Supercomputing Centre in Garching, Germany for more than a month. By applying sophisticated modelling techniques to the 25 Tbytes of stored output, Virgo scientists have been able to recreate evolutionary histories both for the 20 million or so galaxies which populate this enormous volume and for the supermassive black holes which occasionally power quasars at their hearts. By comparing such simulated data to large observational surveys, one can clarify the physical processes underlying the buildup of real galaxies and black holes.
Pictures of the galaxy distributiontop
The top row of the following pictures shows the galaxy distribution in the simulation, both on very large scales, and for a rich cluster of galaxies where one can see them individually. The top right panel hence represents the large-scale light distribution in the Universe. For comparison, the images in the lower row give the corresponding dark matter distributions.
galaxies
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

15. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

16. Constrained Simulations
Initial conditions - Gaussian random fields
Random realization - only power spectrum is assumed
Constrained realizations of Gaussian random fields - construct random realizations which obey any number of (linear) imposed constraints (Hoffman & Ribak 1991)
Use observations to impose the ‘observed universe’ on the initial conditions
=====> Constrained Simulations (CSs) of the Local Universe
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

17. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

18. (~1000 cpu yrs)
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

19. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

20. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

21. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

22. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

23. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

24. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

25. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

26. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

27. Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

28. LG: DM MW
M31
M33
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

29. MW: stars
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

30. M33: stars
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)

31. Constrained Simulations of the Local Universe
Things we don’t know
Galaxy formation
Luminosity function
Structural properties of galaxies
Star formation & its feed back on galaxy formation
Environmental dependance
...
What have we learnt?
How to make DM halos
The distribution of dark matter
The Local Universe appears to be typical - near field cosmology makes sense
The LG in particular appears to be typical: environment, structure of MW & M31’s halo
Constrained Simulations of the Local Universe
Numerical laboratory for galaxy formation experiments, done under realistic conditions
performing near field cosmology on the computer
Yehuda Hoffman (HU) Formation of Local Universe University of Kentucky (Apr 2008)