Makoto Hattori

Substructures Revealed by the Sunyaev-Zel'dovich Effect at 150 GHz in a High-Resolution Map of RX J1347-1145

We report on mapping observations toward the region of the most luminous X-ray cluster RXJ1347-1145 (z=0.45) through the Sunyaev-Zeldovich effect at 21GHz and 150GHz with the Nobeyama 45-m telescope. While a low angular resolution image at 21GHz (beam-size of 76) shows a consistent feature with the ROSAT/HRI X-ray image, a higher angular resolution image (13) at 150GHz reveals complex morphological structures of the cluster region, which cannot be simply described by the spherical isothermal beta-model. If such inhomogeneous morphological features prove to be generic for high redshift clusters, distance measurements to the clusters based on their Sunyaev-Zeldovich data with low angular resolution imaging should be interpreted with caution.

Gravitational Lensing in Clusters of Galaxies

Gravitational lensing in clusters of galaxies is an efficienttool to probe the mass distribution of galaxies and clusters, high redshift objects thanks to the gravitational amplification, and the geometry of the universe. We review some important aspects of cluster lensing and related issues in observational cosmology.

Gas, Iron, and Gravitational Mass in Galaxy Clusters: The General Lack of Cluster Evolution at z < 1.0

We have analyzed the ASCA data of 29 nearby clusters of galaxies systematically, and obtained temperxad atures, iron abundances, and X-ray luminosities of their intracluster medium (ICM). We also estimated the ICM mass using the (3 model, and then evaluated the iron mass contained in the ICM and derived the total gravitating mass. This gives the largest and most homogeneous information about the ICM derived only by ASCA data. We compared these values with those of distant clusters whose temperatures, abundances, and luminosities were also measured with ASCA, and have found no clear evidence of evolution for the clusters at z < 1.0. Only the most distant cluster at z = 1.0, AX J2019.3+1127, has an anomalously high iron abundance, but its iron mass in the ICM may be among normal values for the other clusters, because the ICM mass may be smaller than the other clusters. This may suggest a hint of evolution of clusters at z ~ 1.0.

Detection of Iron Emission Lines from the Galaxy Cluster Including the Radio Galaxy 3C 220.1 at z = 0.62

We have detected an emission-line feature at 4 keV in the X-ray emission from a sky region including the distant radio galaxy 3C 220.1 (z = 0.62) obtained with ASCA. The line energy is 6.1-7.0 keV (90% confidence) in the rest frame of 3C 220.1. Within the present statistics, the observed spectra are consistent with two different models: a nonthermal model consisting of a power-law continuum plus a 6.4 keV iron emission line and a Raymond-Smith thin thermal emission model of kT ~ 6 keV with a metal abundance of ~0.5 solar. However, because of the large (~500 eV) equivalent width of the line, a significant fraction of the X-ray emission is likely to arise from the hot intracluster gas associated with the galaxy cluster that includes 3C 220.1. The spectral parameters of the thermal emission are consistent with the luminosity-temperature relation of nearby clusters.

Spontaneous reduction of the heat conductivity by a temperature gradient-driven instability in electron-ion plasmas

We have shown that there exist low-frequency growing modes driven by a global temperature gradient in electron and ion plasmas, by linear perturbation analysis within the frame work of plasma kinetic theory. The driving force of the instability is the local deviation of the distribution function from the Maxwell-Boltzmann due to a global temperature gradient. Our results suggest that the realization of the global thermal equilibrium is postponed by the local instability which is induced for quicker realization of local thermal equilibrium state in plasmas. The instability provides a new possibility to create and amplify cosmic magnetic fields without the seed for a magnetic field.

Submillimeter detection of the sunyaev - zel'dovich effect toward the most luminous x-ray cluster at z=0.45

We report on the detection of the Sunyaev-Zeldovich (SZ) signals toward the most luminous X-ray cluster RX J1347-1145 at the Nobeyama Radio Observatory (21 and 43 GHz) and with the James Clerk Maxwell Telescope (350 GHz). In particular, the latter is the first successful detection of the SZ temperature increment in the submillimeter band that resolved the profile of a cluster of galaxies. Both the observed spectral dependence and the radial profile of the SZ signals are fully consistent with those expected from the X-ray observation of the cluster. The combined analysis of the 21 and 350 GHz data reproduces the temperature and core radius of the cluster that are determined with ROSAT and ASCA when we adopt the slope of the density profile from the X-ray observations. Therefore, our present data provide the strongest and most convincing case for the detection of the submillimeter SZ signal from the cluster as well as in the Rayleigh-Jeans regime. We also discuss briefly the cosmological implications of the present results.