arXiv subjects

Akihiro Furuzawa

Publications and source records attributed to Akihiro Furuzawa.

38 records · Page 3Linked to original sources

arXiv2001

H0 from an orientation-unbiased sample of SZ and X-ray clusters

We have observed the Sunyaev-Zel'dovich effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the BCS and NORAS cluster catalogues to be well above the surface-brightness limit of the ROSAT All-Sky Survey, and hence to be unbiased with respect to the orientation of the cluster. This controls the major potential systematic effect in the SZ/X-ray method of measureing H0. Taking the weighted geometric mean of the results and including the main sources of random error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity of the clusters, we find H0 = 59 +8/-7 km/s/Mpc assuming a standard CDM model with Omega_M = 1.0, Omega_Lambda = 0.0, or H0 = 65 +8/-7 km/s/Mpc if Omega_M = 0.3, Omega_Lambda = 0.7.

astro-ph↗

arXiv2000

The Observed Mass Profiles of Dark Halos and The Formation Epochs of Galaxies

We have determined the mass profiles of dark halos in 83 objects observed by ASCA. The point spread function of X-ray telescope was deconvoled by the Richardson-Lucy algorithm and the temperature profiles were calculated to obtain the mass profiles. The derived mass profiles are consistent with the NFW model in 0.01-1.0 r_virial. We found a good correlation between the scale radius r_s and the characteristic mass density δ_c, which indicates the self-similarity of dark halos. The spectrum index of primordial density fluctuation, P(k) \propto k^n, was determined from the slope of r_s - delta_c relation. For M_200=10^12-10^15 M_solar, our analysis gives n=-1.2 +/- 0.3 with a confidence level of 90%. The mass density of dark halos is a good indicator of the mean mass density of the universe at the time when the halos were assembled, z=z_f. Assuming delta_c \propto (1+z_f)^3, we have determined the epoch when each dark halo was assembled. Our analysis indicates that the field elliptical galaxies and groups of galaxies formed approximately at 1+z_f ~ 15 and at 1+z_f ~ 7-10 respectively.

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