arXiv subjects

Y. Rephaeli

Publications and source records attributed to Y. Rephaeli.

42 records · Page 3Linked to original sources

arXiv1998

BeppoSAX detection of the Fe K line in the nearby starburst galaxy NGC 253

We present BeppoSAX results on the nearby starburst galaxy NGC 253. Although extended, a large fraction of the X-ray emission comes from the nuclear region. Preliminary analysis of the LECS/MECS/PDS ~0.2-60 keV data from the central 4' region indicates that the continuum is well fitted by two thermal models: a ``soft'' component with kT ~ 0.9 keV, and a ``hard'' component with kT ~ 6 keV absorbed by a column density of ~ 1.2 x10**22 cm-2. For the first time in this object, the Fe K line at 6.7 keV is detected, with an equivalent width of ~ 300 eV. This detection, together with the shape of the 2--60 keV continuum, implies that most of the hard X-ray emission is thermal in origin, and constrains the iron abundances of this component to be ~0.25 of solar. Other lines clearly detected are Si, S and Fe L/Ne, in agreement with previous ASCA results. We discuss our results in the context of the starburst-driven galactic superwind model.

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arXiv1998

BeppoSAX detection of the Fe K line in the starburst galaxy NGC253

Preliminary results obtained from BeppoSAX observation of the starburst galaxy NGC253 are presented. X-ray emission from the object is clearly extended but most of the emission is concentrated on the optical nucleus. Preliminary analysis of the LECS and MECS data obtained using the central 4' region indicates that the continuum is well fitted by two thermal components at 0.9 keV and 7 keV. Fe K line at 6.7 keV is detected for the first time in this galaxy; the line has an equivalent width of ~300eV. The line energy and the shape of the 2-10 keV continuum strongly support thermal origin of the hard X-ray emission of NGC253. From the measurement of the Fe K line the abundances can be unambiguously constrained to ~0.25 the solar value. Other lines clearly detected are Si, S and Fe XVIII/Ne, in agreement with ASCA results.

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arXiv1997

Intracluster Comptonization of the CMB: Mean Spectral Distrortion and Cluster Number Counts

The mean sky-averaged Comptonization parameter, y, describing the scattering of the CMB by hot gas in clusters of galaxies is calculated in an array of flat and open cosmological and dark matter models. The models are globally normalized to fit cluster X-ray data, and intracluster gas is assumed to have evolved in a manner consistent with current observations. We predict values of y lower than the COBE/FIRAS upper limit. The corresponding values of the overall optical thickness to Compton scattering are < 10^{-4} for relevant parameter values. Of more practical importance are number counts of clusters across which a net flux (with respect to the CMB) higher than some limiting value can be detected. Such number counts are specifically predicted for the COBRAS/SAMBA and BOOMERANG missions.

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arXiv1997

Measurement of the Hubble Constant from X-ray and 2.1 mm Observations of Abell 2163

We report 2.1 mm observations of the Sunyaev-Zel'dovich (S-Z) effect; these observations confirm our previous detection of a decrement in the Cosmic Microwave Background intensity towards the cluster Abell 2163. The S-Z data are analyzed using the relativistically correct expression for the Comptonization. We begin by assuming the intracluster (IC) gas to be isothermal at the emission weighted average temperature determined by a combined analysis of the ASCA and GINGA X-ray satellite observations. Combining the X-ray and S-Z measurements, we determine the Hubble constant to be H_0(q_0=0.5)= 60 +40/-23 km/s/Mpc, where the uncertainty is dominated by the systematic difference in the ASCA and GINGA determined IC gas temperatures. ASCA observations suggest the presence of a significant thermal gradient in the IC gas. We determine $H_0$ as a function of the assumed IC gas thermal structure. Using the ASCA determined thermal structure and keeping the emission weighted average temperature the same as in the isothermal case, we find H_0(q_0=0.5)= 78 +54/-28 km/s/Mpc. Including additional uncertainties due to cluster asphericity, peculiar velocity, IC gas clumping, and astrophysical confusion, we find H_0(q_0=0.5)= 78 +60/-40 km/s/Mpc.

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arXiv1997

Limits on the Peculiar Velocities of Two Distant Clusters Using the Kinematic Sunyaev-Zel'dovich Effect

We report millimeter-wavelength observations of the Sunyaev-Zel'dovich (S-Z) effect in two distant galaxy clusters. A relativistically correct analysis of the S-Z data is combined with the results of X-ray observations to determine the radial peculiar velocities v_r of the clusters. We observed Abell 2163 (z=.201) in three mm-wavelength bands centered at 2.1, 1.4, and 1.1 mm. We report a significant detection of the thermal component of the S-Z effect seen as both a decrement in the brightness of the CMB at 2.1 mm, and as an increment at 1.1 mm. Including uncertainties due to the calibration of the instrument, distribution and temperature of the IC gas, and astrophysical confusion, a simultaneous fit to the data in all three bands gives v_r=+490 +1370/-880 km/s at 68% confidence. We observed Abell 1689 (z=.181) in the 2.1 and 1.4 mm bands. Including the same detailed accounting of uncertainty, a simultaneous fit to the data in both bands gives v_r=+170 +815/-630 km/s. The limits on the peculiar velocities of A2163 and A1689 correspond to deviations from the uniform Hubble flow of <= 2-3%.

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arXiv1996

A Millimeter/Submillimeter Search for the Sunyaev-Zel'dovich Effect in the Coma Cluster

Observations from the first flight of the Medium Scale Anisotropy Measurement (MSAM1-92) are analyzed to search for the Sunyaev-Zel'dovich (SZ) effect towards the Coma cluster. This balloon-borne instrument uses a $28\arcmin$ FWHM beam and a three position chopping pattern with a throw of $\pm40\arcmin$. With spectral channels at 5.7, 9.3, 16.5, and 22.6~\icm, the observations simultaneously sample the frequency range where the SZ spectral distortion in the intensity transitions from a decrement to an increment and where the fractional intensity change is substantially larger than in the Rayleigh-Jeans region. We set limits on the Comptonization parameter integrated over our antenna pattern, $Δy \leq 8.0 \times 10^{-5}$($2 σ$). For a spherically symmetric isothermal model, this implies a central Comptonization parameter, $y_o \leq 2.0 \times 10^{-4}$, or a central electron density, $n_o \leq 5.8 \times10^{-3}$cm$^{-3}h_{50}$, a result consistent with central densities implied by X-ray brightness measurements and central Comptonization estimates from lower frequency observations of the SZ effect.

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