High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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CLUSTER RESEARCH WITH X-RAY OBSERVATIONS
CLUSTER RESEARCH WITH X-RAY OBSERVATIONS
Pages 112-133
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From page 112... ...
1972~. Subsequent spectroscopic studies detected X-ray emission lines of highly ionized iron and demonstrated that the X-ray emission was produced by thermal radiation of a hot gas with temperatures in the range of 30 to 100 million degrees (Mitchell et al.
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From page 113... ...
, will include both optically defined classes of rich clusters (such as Abell or Zwicky) as well as poorer clusters or any gravitationally bound system of galaxies containing high-temperature gas.
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From page 114... ...
114 m~ to WE E id| c,,E E CJ Al ,C of s-~ ~ ~hi' Cot ~ ~ 8 ~ ~E ~8 - °
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From page 115... ...
a correlation between X-ray luminosity and temperature ~Iusho~zky 1988~. In our recent work we have investigated the statistical properties of the 226 Abell clusters with z < 0.15 observed by the Einstein Observatory (Burg et al.
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_ ~ x J g O _ U AMERICAN AND SOVIET PERSPECTIVES o o ~ V 0.01 0.05 0.1 o.5 redshift FIGURE 1 Scatter diagram of X-ray luminosity versus redshift for richness 1 clusters.
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From page 117... ...
has shown that richness 0 clusters are incomplete by a factor of > 3. Quantitatively we fit Schechter functions to the data with the results shown in Figure 2b.
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From page 118... ...
d. Our observed luminosity functions can be described as Schechter functions with approximately the same slope and different L~*
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From page 119... ...
We agree at the high-luminosity end with previous results and we are not inconsistent at the low-luminosity end where use of the Bahcall normalization, to take into account R = 0 incompleteness, has the biggest effect. As mentioned above, the X-ray luminosity which we measure must be in all cases the sum of the X-ray luminosity of the individual galaxies plus a component due to intergalactic hot dense gas.
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From page 120... ...
This is evidence that there is a substantial number of clusters in which the X-ray emission from intracluster gas is not dominant. INTERPRETATION OF THE LUMINOSlXY FUNCTION Studying the wide range of X-ray luminosity of clusters selected by richness class (presumably therefore of given total mass)
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From page 121... ...
Specifically we can attempt to separate out the factors which determine the X-ray emission and relate them to initial conditions and dynamic evolution of the cluster. Using the thermal bremmstrahlung expression we can wnte: Lo ~ PgasM gaSTg/s Using the vinal theorem and equipartition we can relate T,a5 to the vinal gas mass, Mv, and density, pv, kT~ GMV Rv GM., MV ~ \4~PV J or To M213pi/3 and Lo ~ PgasMgasMv Pv
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From page 122... ...
This results in an expression for Lo of the form LO = A.,a+b+cM< in which a represents the cosmological term, b the dynamical term, and c the gas injection or stripping mechanisms. In summary: The X-ray emission of a cluster depends not only on its mass but also on the initial conditions, the subsequent dynamical evolution of the system and the mechanism and history of the gas injection.
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Future missions such as ASTRO-D, Jet X and XMM will yield spectra with some angular resolution for the nearest systems but only integral luminosity and integral spectra for the more distant ones. Only with AXAF will one have
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From page 124... ...
. Diameter 84 cm 120 cm diameter Number of surfaces 4 6 field of view 2 degrees l degree geometric area 1141 Cm2 1700 cm2 Angular resolution Center of field ~3" - ~.5" 8' off axis ~5" ~3.5,, 30' off ems ~60" ~60,' Imaging Instruments (field, spectral resolution)
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From page 125... ...
high-anguLdr resolution coupled with spectral resolution for the most distant detectable clusters (A z ~ 1~. The ROSAT all-sky survey is an important precursor to AXAF.
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From page 126... ...
evolution of the luminosity function evolution of metallicity Cluster formation and cosmology dark mass correlation functions protoclusters primordial gas Zeldovich-Sunyaev effect, Krolik-Raymond method: Ho, qO clusters at 0.5 < z < 1.0. However, the angular resolution of the PSPC, the detector with which the survey will be conducted, is of order ~ 30" and except for nearby clusters (z < 0.2)
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From page 127... ...
Of particularly interesting clusters with HRI high angular resolution observations capable of resolving the details of the cluster morphology. This classification technique relies on utilizing all available X-ray and optical information and the observational constraints derived from the MSS survey to divide the ROSAT survey sources into appropriate bins.
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From page 128... ...
1990~. · A flux limited X-ray survey for all types of clusters defined as gravitationally bound systems of galaxies containing intracluster gas with a high degree of metallicity and central condensation.
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From page 129... ...
· Confrontation between model-predicted redshift distn~ut~ons and observed redshift distn~utions for optically characterized subsamples. The tremendous advantage of AXAF with respect to ROSAT is glen by two specific technical improvements coupled together: the high~uantum efficiency and spectral resolution of the CCD detectors coupled to a highangular resolution telescope.
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From page 130... ...
AXAF therefore possesses He angular resolution and spectroscopic capability to directly determine the angular extent of a cluster as well as the ability to directly measure its redshift (if the X-ray emitting gas is enriched)
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From page 131... ...
and by studying the z distribution of carefully selected subsamples. However, the causes for the apparent evolutionary effects, if any, will be difficult to determine.
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From page 133... ...
a Similar measurements can be extended by AXAF to very large redshifts, from z > 0.25 to z of order of ~ When this program is completed there will emerge a new understanding of the formation and evolution of these objects, among the most massive gravitationally bound structures in the Universe. Furthermore, we hope this will lead to a more complete picture of the structure of the Universe.
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