Observational Cosmology

Understanding the nature and origin of large-scale structure in the Universe is one of most compelling issues in observational cosmology. The currently most conventional scenario is given by the cold dark matter (CDM) dominated model, where gravitational instability mainly driven by spatial inhomogeneities of CDM distribution amplifies the seed density perturbations to form the present-day hierarchical structures. Therefore revealing distribution and amount of CDM is crucial to understanding the formation of large-scale structure. In addition the presence of dark energy drives the accelerating cosmic expansion, and therefore affects the growth of structure formation. The dark matter distribution and the nature of dark energy can be explored from massive galaxy surveys. We have worked on measurements from current surveys and are actively involved in the planning and design of the future survey with Subaru Telescope, 8.2 meter optical-infrared telescope at the summit of Mauna Kea (4,200m), Hawaii.

Weak gravitational lensing:

The path of light ray emitted by a distant galaxy is bent by gravitational force of intervening large-scale structure during the propagation, causing the image to be distorted - the so-called weak lensing shear. Conversely, measuring the coherent shear signals between galaxy images allows us to reconstruct the distribution of invisible dark matter. Moreover, since the weak lensing shear deals with the light propagation on cosmological distance scales, the lensing strengths depend on the cosmic expansion history that is sensitive to the nature of dark energy. Thus weak lensing based observables offer a powerful way for studying the nature of invisible components, dark matter and dark energy. We are carrying out observational and theoretical studies of weak lensing phenomena using our own Subaru data sets as well as simulations of large-scale structure.

Hyper Suprime Camera (HSC):

The HSC, currently under construction, is the project to replace the prime focus camera of Subaru Telescope with a new camera that has wider field-of-view than the current one by a factor of 10. Fully utilizing the unique capabilities of HSC, its survey speed and excellent image quality, we are planning and designing a massive galaxy survey that covers an area of a few thousands square degrees and reaches to the depth to probe the Universe up to redshifts of a few. In fact these data sets will provide us an ideal data sets for exploring the nature of dark matter and dark energy via measurements of cosmological observables available from the data, weak lensing and galaxy clustering statistics. We, IPMU members, are actively involved in this HSC project, and working on the designing and planning of HSC galaxy survey and development of data analysis pipeline.

Sloan Digital Sky Survey III:

Over the next six years (2008-2014), the SDSSIII will exploit the unique wide-field spectroscopic capability of the Apache Point Observatory's 2.5-meter telescope, extending the previous SDSS surveys to a deeper universe with the improved spectrograph. We, IPMU members, are involved in SDSSIII and can freely access to the data sets before the public data release. In particular, one of the planned surveys, the Baryon Oscillation Spectroscopic Survey (BOSS) will map the spatial distribution of luminous galaxies and quasars to detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe. Using the acoustic scale as a standard ruler, we can infer the angular diameter distance to the galaxy redshift, thereby enabling to test the models of dark energy. We are planning to develop an optimal method for measuring properties of galaxy clustering in order to obtain unbiased estimates on the acoustic scale as well as on cosmological parameters.

Group Members

Yen-Ting Lin

Formation and evolution of galaxies. Roles of galactic mergers and feedback from supermassive blackholes on the formation of giant galaxies. Data analysis of BOSS survey and radio surveys to elucidate the phenomenon of radio-loud active galactic nuclei. Evolutionary connections between galaxies at z=0 and z=1 using future HSC data.

Issha Kayo

Extraction of cosmological information from the large-scale structure of the Universe, particularly using the actual data taken by the Sloan Digital Sky Survey and virtual data generated by N-body simulations. Construction of a homogeneous catalog of gravitationally lensed quasars to constrain the dark energy.

Tsz Yan Lam

Galaxy surveys to constrain cosmological models. Large-scale structure probes of primordial non-Gaussianity.

Keiichi Maeda

Supernova cosmology, especially in the evaluation of applicability of Type Ia supernovae as cosmological distance indicators.

Takaya Nozawa

Evolution of dust throughout the cosmic history. Evaluation of the impacts of dust on the observational cosmology using Type Ia supernovae as a standard candle.

Jan Schuemann

Study of neutrino fluxes and their origin using Super-Kamiokande. Improving the Super-Kamiokande by adding Gadolinium.

Naoshi Sugiyama

Investigation of the Cosmic Microwave Background. Testing of dark energy models using observational data such as the baryon acoustic oscillation and gravitational lensing.

Masahiro Takada

Observational and theoretical studies of gravitational lensing caused by hierarchical structures of the universe. Nature of dark side of the universe, dark matter and dark energy, with the gravitational lensing observables. Future Subaru Weak Lensing Survey.

Atsushi Taruya

Modeling dynamics and statistics of large-scale structure of
the Universe, and testing various cosmological scenarios and/or hypothesis through direct comparison between theory and observations. A pursuit of the prospects for future observations such as HSC and BOSS to constrain dark energy, massive neutrinos, primordial non-Gaussianity as well as to test theory of gravity.

Jun'ichi Yokoyama

Analysis of CMB anisotropy.

Naoki Yoshida

Large galaxy surveys and weak lensing observations. Computer simulations to generate a large number of mock catalogues for future observational programs.