arXiv subjects

Kohji Yoshikawa

Publications and source records attributed to Kohji Yoshikawa.

40 records · Page 3Linked to original sources

arXiv1999

Cosmological Implications of Galaxy Clusters in X-Ray, Millimeter, and Submillimeter Bands

Cosmological implications of clusters of galaxies are discussed with particular attention to their importance in probing the cosmological parameters. More specifically we compute the number counts of clusters of galaxies, Log $N$ -- Log $S$ relation, in X-ray and submm bands on the basis of the Press--Schechter theory. As an important step toward breaking the degeneracy among the viable cosmological models, we observed the most luminous X-ray cluster RXJ1347-1145 in three bands (21 and 43 GHz in the Nobeyama Radio Observatory, Japan, and 350 GHz in the J. C. Maxwell telescope at Mauna Kea, Hawaii). We report on the preliminary results which are in good agreement with the profile of the Sunayev -- Zel'dovich effect predicted on the basis of the previous X-ray observation of the cluster.

astro-ph↗

arXiv1999

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 -- Zel'dovich (SZ) signals toward the most luminous X-ray cluster RXJ1347-1145 at Nobeyama Radio Observatory (21 and 43 GHz) and at James Clerk Maxwell Telescope (350 GHz). In particular the latter is the first successful detection of the SZ temperature increment in the submillimeter band which 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 21GHz and 350GHz data reproduces the temperature and core-radius of the cluster determined with the ROSAT and ASCA satellites 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.

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arXiv1998

Reconstructing the radial profiles of gas density and temperature in clusters of galaxies from high-resolution X-ray and radio observations

We describe a non-parametric method to reconstruct gas density and temperature profiles of galaxy clusters from observations of X-ray surface brightness, emission-weighted temperature and the y-parameter through the Sunyaev-Zel'dovich effect. This method is based on the inversion of the projected profiles under the spherically symmetric approximation, which is independent of the equation of state of cluster gas and does not assume that the gas is in hydrostatic equilibrium. In particular we examine the reliability of the reconstruction method assuming a few theoretical models for cluster gas and assigning the statistical errors expected for future X-ray and radio observations. We also discuss briefly the effect of non-sphericity on the basis of simulated clusters.

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arXiv1998

Hydrodynamical Simulation of Clusters of Galaxies in X-Ray, mm, and submm Bands: Determination of Peculiar Velocity and the Hubble Constant

We have performed a series of simulations of clusters of galaxies on the basis of the smoothed particle hydrodynamics technique in a spatially-flat cold dark matter universe with $Ω=0.3$, $λ=0.7$, and H_0=70 km/s/Mpc as one of the most successful representative cosmological scenarios. In particular, we focus on the Sunyaev--Zel'dovich effect in submm and mm bands, and estimate the reliability of the estimates of the global Hubble constant $H_0$ and the peculiar velocity of clusters $v_r$. Our simulations indicate that fractional uncertainties of the estimates of $H_0$ amount to $\sim 20%$ mainly due to the departure from the isothermal and spherical gas density distribution. We find a systematic underestimate bias of $H_0$ by $\sim 20%$ for clusters $z\approx 1$, but not at $z\approx 0$. The gas temperature drop in the central regions of our simulated clusters leads to the underestimate bias of $v_r$ by $\sim 5%$ at $z\approx 0$ and by $\sim 15%$ at $z\approx 1$ in addition to the statistical errors of the comparable amount due to the non-spherical gas profile.

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