An X-Ray Survey of Clusters of Galaxies with the Einstein Observatory and a Study of Iron Sedimentation in the Intracluster Gas.
Abstract
A sample of 74 clusters of galaxies has been observed in the soft X-ray band with the HEAO-2 satellite, also known as the Einstein Observatory. The measurements of the X-ray luminosities and the X-ray core radii have been compared with optical and radio parameters. The correlations that have been found favor thermal bremsstrahlung from a hot intracluster gas as the dominant emission mechanism. In addition, there is evidence that a significant fraction of the intracluster gas has its origin inside the galaxies, and is removed from the galaxies by ram pressure. The cluster observations were used to determine the X-ray luminosity function of clusters of galaxies. The results agree with previous measurements. Assuming a reasonable form for the evolution of the X-ray luminosity of the typical cluster, a background contribution from clusters has been determined and is about 10% of the soft X-ray background in the 0.5-4.0 keV band. If the condition of thermodynamic equilibrium is imposed on the intracluster gas, then one would expect to find the heavy elements concentrated in the cluster center. If such a model is correct, then the iron abundance as estimated from the strength of the 7 keV iron line is overestimated by nearly an order of magnitude. The density and emission profiles for such an equilibrated intracluster gas are calculated. The thermal bremsstrahlung profile is consistent with the X-ray data of the Coma cluster, a highly evolved nearby cluster. Finally, the X-ray ellipticities and position angles of the clusters are determined and compared with the optical values, when available. The relationship between the X-ray and optical parameters is consistent with the thermal bremsstrahlung model, with the intracluster gas in equilibrium in the gravitational potential well of the cluster. The X-ray contours of the Coma cluster indicates that the cluster is oblate rather than prolate, consistent with the hypothesis that protoclusters are formed out of gravitational instabilities in the early universe.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1983
- Bibcode:
- 1983PhDT.........1A
- Keywords:
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- Physics: Astronomy and Astrophysics;
- Bremsstrahlung;
- Galactic Clusters;
- Intergalactic Media;
- Stellar Cores;
- Stellar Luminosity;
- X Ray Spectra;
- Abundance;
- Heao 2;
- Iron;
- Thermodynamic Equilibrium;
- Astronomy