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Register a new userA measurement of H_0 from Ryle Telescope, ASCA and ROSAT observations of Abell 773
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We present new Ryle Telescope (RT) observations of the Sunyaev Zeldovich (SZ) decrement from the cluster Abell 773. The field contains a number of faint radio sources that required careful subtraction. We use ASCA observations to measure the gas temperature and a ROSAT HRI image to model the gas distribution. Normalising the gas distribution to fit the RT visibilities returns a value of H_0 of 77 (+19,-15) km/s/Mpc (1-sigma errors) for an Einstein-de-Sitter universe, or 85 (+20,-17) km/s/Mpc for a flat model with Omega_Lambda = 0.7. The errors quoted include estimates of the effects of the principal errors: noise in the SZ measurement, gas temperature uncertainty, and line-of sight depth uncertainty.
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We describe our algorithm for measuring the Hubble constant from Ryle Telescope (RT) interferometric observations of the Sunyaev-Zeldovich (SZ) effect from a galaxy cluster and observation of the cluster X-ray emission. We analyse the error budget in this method: as well as radio and X-ray random errors, we consider the effects of clumping and temperature differences in the cluster gas, of the kinetic SZ effect, of bremsstrahlung emission at radio wavelengths, of the gravitational lensing of background radio sources and of primary calibration error. Using RT, ASCA and ROSAT observations of the cluster Abell 1413, we find that random errors dominate over systematic ones, and estimate H_0 = 57^{+23}_{-16} km/s/Mpc (1-sigma errors).
The results obtained from the ASCA observations of the cluster of galaxies Abell 3627 are presented. This cluster, located behind the Milky way, was recently found to be a nearby, X-ray bright and very rich cluster. Pointed observations onto the central region of the cluster gave a gas temperature of $sim7$ keV and a metallicity of about 0.2 solar. An offset pointing to a substructure elongated to south-east of the cluster center gave a significantly lower temperature of $sim 5$ keV. The 2--10 keV luminosity within a radius of 40 (1.1 Mpc) is estimated to be $3.7 times 10^{44} erg/s$. The X-ray data imply a cluster mass of about $4times 10^{14}$ $M_odot$ within 40.
We present ROSAT (HRI and PSPC) and ASCA observations of the two luminous (L_x ~10^{41-42} erg s^{-1}) star-forming galaxies NGC3310 and NGC3690. The HRI shows clearly that the sources are extended with the X-ray emission in NGC3690 coming from at least three regions. The combined 0.1-10 keV spectrum of NGC3310 can be described by two components, a Raymond-Smith plasma with temperature kT=0.81^{+0.09}_{-0.12} keV and a hard power-law, Gamma=1.44^{+0.20}_{-0.11}, (or alternatively a harder Raymond-Smith plasma with kT ~15 keV), while there is no substantial excess absorption above the Galactic. The soft component emission is probably due to a super-wind while the nature of the hard emission is more uncertain with likely origins, X-ray binaries, inverse Compton scattering of IR photons, an AGN or a very hot gas component (~10^8 K). The spectrum of NGC3690 is similar, with kT=0.83^{+0.02}_{-0.04} keV and Gamma=1.56^{+0.11}_{-0.11}. We also employ more complicated models such as a multi-temperature thermal plasma, a non-equilibrium ionization code or the addition of a third softer component which improve the fit but not at a statistically significant level (<2sigma). These results are similar to recent results on the archetypal star-forming galaxies M82 and NGC253.
We present the analysis of archival data from ROSAT and ASCA of a serendipitous source PKS 2316-423. According to its featureless non-thermal radio/optical continuum, the object has been assumed as a BL Lac candidate in the literature. It was evident variable over the multiple X-ray observations. Specially, a variable high-energy tail of the synchrotron radiation is revealed. X-ray spectral analysis provided further evidence of its synchrotron-nature broad-band spectrum with steep and down-curved shape in the range of 0.1-10 keV. Further SED analysis suggest that it is a very low luminosity ``intermediate or high energy peaked BL Lac object. Given the unusual low luminosity, the further studies of PKS 2316-423 might give clues on the evolution properties of BL Lacs.
We calibrate the galaxy cluster mass - temperature relation using the temperature profiles of intracluster gas observed with ASCA (for hot clusters) and ROSAT (for cool groups). Our sample consists of apparently relaxed clusters for which the total masses are derived assuming hydrostatic equilibrium. The sample provides data on cluster X-ray emission-weighted cooling flow-corrected temperatures and total masses up to r_1000. The resulting M-T scaling in the 1-10 keV temperature range is M_1000 = (1.23 +- 0.20)/h_50 10^15 Msun (T/10 keV)^{1.79 +- 0.14} with 90% confidence errors, or significantly (99.99% confidence) steeper than the self-similar relation M propto T^{3/2}. For any given temperature, our measured mass values are significantly smaller compared to the simulation results of Evrard et al. (1996) that are frequently used for mass-temperature scaling. The higher-temperature subsample (kT > 4 keV) is consistent with M propto T^{3/2}, allowing the possibility that the self-similar scaling breaks down at low temperatures, perhaps due to heating by supernovae that is more important for low-temperature groups and galaxies as suggested by earlier works.
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