Astrophysics / Cosmology
Understanding the universe through computational simulations
Test of Cosmological Models
Cosmological Parameters
We are now entering into a precision cosmology meaning that the cosmological parameters are measured to a few percent level of precision. The advent of the precision cosmology may be possible owing to the recent CMB (Cosmic Microwave Background) and LSS (Large-scale Structure) observations. The WMAP observed relic photons from the CMB photosphere created 300,000 years after the Big Bang. Also the Planck observatory is going to measure the CMB anisotropy with an unprecedented precision. Also various LSS observations such as the SDSS (Sloan Digital Sky Survey) and 2dF (two degree Field) galaxy survey measured distribution of galaxies which may help us understand the nonlinear evolution of matter content until the recent epoch. In the next decade many galaxy redshift survey projects are going to pile a huge amount of galaxy information which will be used to pin down the parameter values of our universe.
Dark Energy and Dark Matter
Now we believe that our universe mainly consists of two mysterious physical ghosts: Dark Energy and Dark Matter. The Dark energy occupies 74% of the total energy of the universe and the dark matter takes about 20%. Only 4% of total energy exists in form of the baryonic matter or ordinary elementary particles. The Dark Energy is now guessed to be the cosmological constant which was proposed by A. Einstein. But various hypothetical models are proposed and we hope to discriminate their effects on the matter distribution in the forthcoming years. Also the Dark Matter has been unknown to us until now and many high energy particle projects are now and will be in operation to directly and indirectly detect its signature.
Test Inflationary Models
The current concordance world model is based on the inflationary theory which predicts the Gaussian distribution of the matter density. While the current CMB observation is consistent with the inflationary theory, some people argued to find the non-Gaussianity in the CMB anisotropy. Many researches are studying many non-Gaussian theories and their effects on the CMB anisotropy and LSS distributions, and we are going to study their effects on the matter distribution using cosmological simulations.
Test of Galaxy Formation Theory
Mass Build-up History
From the CDM (Cold Dark Matter) power spectrum, we know that the cosmic structure evolves hierarchically which means that cosmic objects grow in mass and size by merging nearby smaller objects. This mass-built up history of the virialized objects can be compared with the galaxy and cluster observations. We are studying the mass buildup history using various semi-analytic modeling and halo occupation distribution models.
Star Formation History
Star formation plays a very important role in the nonlinear matter evolution of the universe. From the nearly homogeneous backgrounds, small density fluctuations gravitationally grow until they reach a critical point when it starts to trigger the hydrogen burning. Before the star formation the universe was believed to be dark. But as the matter fluctuation grows, first stars began to emit photons which may reionize the neutral hydrogen in the low density medium and the universe began to be transparent in the visible band. In the high density regions globular clusters and dwarf galaxies are believed to first form and their hierarchical merging process made larger virialized structures such as galaxies and clusters. We are going to investigate the star formation history from various models and test the models against astronomic observations.
Galaxy Morphology
Galaxy morphology has been a great debate over the last 100 years. E. Hubble classified galaxies into several morphological groups linking them like the Hubble tuning fork. While the mechanism to derive the galaxy shape has not been known until now, we are now able to get some statistical evidences from the large size of the galaxy survey data.