19 research outputs found
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 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
Erratum: Properties of the X-ray-brightest Abell-type clusters of galaxies (XBACs) from ROSAT All-SKy Survey data - I. The sample
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 (), the nominal redshift range of the ACO catalogue of ,
and X-ray fluxes above erg cm s 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
The X-ray morphology of the relaxed cluster of galaxies A2256. I - Evidence for a merger event
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