DT/T beyond linear theory

The major contribution to the anisotropy of the temperature of the Cosmic Microwave Background (CMB) radiation is believed to come from the interaction of linear density perturbations with the radiation previous to the decoupling time. Assuming a standard thermal history for the gas after recombination, only the gravitational field produced by the linear density perturbations present on a $\Omega\neq 1$ universe can generate anisotropies at low z (these anisotropies would manifest on large angular scales). However, secondary anisotropies are inevitably produced during the nonlinear evolution of matter at late times even in a universe with a standard thermal history. Two effects associated to this nonlinear phase can give rise to new anisotropies: the time-varying gravitational potential of nonlinear structures (Rees-Sciama RS effect) and the inverse Compton scattering of the microwave photons with hot electrons in clusters of galaxies (Sunyaev-Zeldovich SZ effect). These two effects can produce distinct imprints on the CMB temperature anisotropy. We discuss the amplitude of the anisotropies expected and the relevant angular scales in different cosmological scenarios. Future sensitive experiments will be able to probe the CMB anisotropies beyong the first order primary contribution.Comment: plain tex, 16 pages, 3 figures. Proceedings of the Laredo Advance School on Astrophysics "The universe at high-z, large-scale structure and the cosmic microwave background". To be publised by Springer-Verla

Properties of the X-ray-brightest Abell-type clusters of galaxies (XBACs) from ROSAT All-Sky Survey data - I. The sample

We present an essentially complete, all-sky, X-ray flux limited sample of 242 Abell clusters of galaxies (six of which are double) compiled from ROSAT All-Sky Survey data. Our sample is uncontaminated in the sense that systems featuring prominent X-ray point sources such as AGN or foreground stars have been removed. The sample is limited to high Galactic latitudes ($|b| \geq 20^{\circ}$), the nominal redshift range of the ACO catalogue of $z \leq 0.2$, and X-ray fluxes above $5.0 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ in the 0.1 -- 2.4 keV band. Due to the X-ray flux limit, our sample consists, at intermediate and high redshifts, exclusively of very X-ray luminous clusters. Since the latter tend to be also optically rich, the sample is not affected by the optical selection effects and in particular not by the volume incompleteness known to be present in the Abell and ACO catalogues for richness class 0 and 1 clusters. Our sample is the largest X-ray flux limited sample of galaxy clusters compiled to date and will allow investigations of unprecedented statistical quality into the properties and distribution of rich clusters in the local Universe.Comment: LaTeX file, 21 pages, 28 PostScript figures, MN style and EPSF macros included, accepted for publication in MNRA

The position sensitive proportional counter (PSPC) of the ROSAT telescope

To appear in the Transactions of the Sixth Symposium on X-and Gamma-Ray Sources and Applications in Nuclear Instruments and MethodsSIGLETIB: RN 9303 (32) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

ROSAT observations of distant optically-selected galaxy clusters

Evolution of the X-ray cluster luminosity function (XLF) has been investigated through X-ray observations of distant optically-selected galaxy clusters. A subset of 14 clusters provides a statistically complete sample with mean redshift anti z=0.42, and a typical Abell richness of class 1-2. Observations of 12 of these clusters were secured using the ROSAT satellite in pointed mode; the remaining two clusters have been analysed using data from the All Skky Survey. The X-ray emission from these clusters is surprisingly weak. The cluster luminosities are less than 5x10"4"3 erg/s in all but two cases. We use a maximum likelihood method to perform a quantitative comparison between our distant cluster luminosities and the present-day X-ray luminosity function derived from the Einstein Extended Medium Sensitivity Survey (EMSS). In the simplest case, where there is a direct relationship between optical richness and X-ray luminosity, our results imply a rise in the amplitude of the luminosity function by almost an order of magnitude since z#approx =#0.4. Even allowing for a significant scatter in the richness-L_X correlation, as observed locally, the distant data are inconsistent with the present-day luminosity function at the 3#sigma# level. Our ROSAT data thus confirm the negative evolution of the luminosity function seen in the Einstein EMSS survey and suggest that the steep slope in the high redshift function may flatten off at luminosities below 10"4"4 erg/s. (orig./HM)Available from TIB Hannover: RN 9303(278) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman