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Research Interests |
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 SZ effect and gravitational lensing by clusters of galaxies | | In hierarchical structure formation models, such as the Cold Dark Matter (CDM) model, clusters are formed from hierarchical clustering of smaller units that have previously collapsed. Such merger events are thus central to theories of cluster formation. The study of clusters in non-relaxed states, and of potential merger events, has been one of the major research fields in recent years. SZ cluster observations combined with optical and weak lensing observations will make it possible to understand quantitatively the formation of large scale structures in the universe. SZ observations with AMiBA will enable us to detect the hot ICM in clusters, the measurement of image distortions of background galaxies induced by the gravitational lensing effect with CFHT/MEGACAM will make it possible to reconstruct the distribution of dark matter, and the detection of galaxies with MEGACAM will allow us to pinpoint galaxies with respect to gravitational structures (Umetsu et al. 2004, MPLA, 19, 1027; Umetsu et al. 2005, astro-ph/0506065). |
| Mergers and non-thermal SZ effect | | XMM-Newton and Chandra reveal detailed structures and dynamical processes
in clusters of galaxies. The SZ effect is a potential tool to study these
substructures in more details for even very distant clusters. An analytical
model can give information on the influence of an ongoing merger on the thermal
SZ effect. It is expected that the spectral shape of the SZ effect is distorted
due to the higher fraction of relativistic electrons, and also the pressure
distribution in the cluster changes. Mapping this non-thermal SZ effect in
such a region will set constraints on merger dynamics and it might reveal
mergers which are not visible in X-rays. Observations out to hight redshift canfurther constrain the merger number counts and the structure formation scenarios. |
| Reionization history of the universe, and cosmological quintessence | | Reionization and polarization
Reionizaiton history of the universe is still one of the puzzle in
the cosmology. The polarization of Cosmic Microwave Background
(CMB) is supposed to answer the question since it is sensitive on
the existence of free electron. Furthermore, the "Sunyaev Zel'dovich
effect like polarization" gives us information of reionization
algorithm in smaller scales.
Cosmological quintessence
Several theories of fundamental physics
predict the existence of scalar fields or quintessence. A slowly
rolling scalar field may mimic the behavior of cosmology
constant. And the perturbations of the scalar filed may give effects
on CMB angular power spectrum and structure formation. Furthermore,
the field is expected to be coupled with matter, unless some
unknown symmetry prevents it. Such kind of coupling can be
constrained by varying fine structure from quasar absorption spectra
(S. Lee et al. 2004) or CMB experiments(S. Lee and G.C Liu in
preparation). |
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