Elemental Abundances via X-ray Observations of Galaxy Clusters and the InFOCuS Hard X-ray Telescope
Elemental Abundances via X-ray Observations of Galaxy Clusters and the InFOCuS Hard X-ray Telescope
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Date
2004-04-30
Authors
Baumgartner, Wayne
Advisor
Mushotzky, Richard F
Leventhal, Marvin
Leventhal, Marvin
Citation
DRUM DOI
Abstract
The first part of this dissertation deals with the oxygen abundance of
the Milky Way interstellar medium. Previous measurements had shown
that oxygen in the ISM was depleted compared to its abundance in the
sun. This dissertation presents new measurements of the ISM oxygen
abundance taken in the X-ray band by observing the oxygen 0.6 keV
photoionization K-edge in absorption towards 10 galaxy clusters.
These measurements show that the ISM oxygen abundance is 0.9 solar,
much greater than earlier depleted values. The oxygen abundance is
found to be uniform across our 10 lines of sight, showing that it is
not dependent on the depth of the hydrogen column. This implies that
the galactic oxygen abundance does not depend on density, and that it
is the same in dense clouds and in the more diffuse ISM.
The next part of the dissertation measures elemental abundances in the galaxy clusters themselves. The abundances of the elements iron,
silicon, sulfur, calcium, argon, and nickel are measured using the
strong resonance K-shell emission lines in the X-ray band. Over 300
clusters from the ASCA archives are analyzed with a joint fitting
procedure to improve the S/N ratio and provide the first average
abundance results for clusters as a function of mass. The alpha
elements silicon, sulfur, argon and calcium are not found to have
similar abundances as expected from their supposed common origin.
Also, no combination of SN Ia and SN II yields can account for the
cluster abundance ratios, perhaps necessitating a contribution from a
cosmologically early generation of massive population III stars.
The last part of this dissertation details the development of the
Cadmium Zinc Telluride (CZT) detectors on the InFOCuS hard X-ray
telescope. InFOCuS is a balloon-borne imaging spectrometer that
incorporates multi-layer coated grazing-incidence optics and CZT
detectors. These detectors are well suited for hard X-ray astronomy
because their large bandgap and high atomic number allow for efficient room temperature detection of photons in the 20-150 keV band. The InFOCuS CZT detectors achieve an energy resolution of 4.0 keV. A 2000 flight to measure the inflight background is discussed, as well as the results of a 2001 flight to observe Cyg X-1.