Chandra X-ray constraints on normal and starburst galaxies at cosmologically interesting distances
Abstract
This thesis concerns the characterization of a population of normal and starburst galaxies within the 1 million second Chandra Deep Field-North (CDF-N) survey field. Constraints are placed both on the individually undetected objects (the majority of the field population at z ≳ 0.3) and the individually X-ray detected objects. The individually X-ray detected normal and starburst galaxies are observationally distinguishable from the AGN through their very low X-ray to optical flux ratios; they are referred to as optically bright, X-ray faint (OBX) sources. This X-ray study represents a new area of research in that for the first time it is possible to detect normal and starburst galaxies at cosmologically interesting look-back times (i.e. billion of years). The first part of the thesis concerns multiwavelength studies of normal and starburst galaxies, focusing on the new X-ray data. These analyses are carried out based on CDF-N X-ray exposures <500 ks. I discuss the first instances of discoveries of normal galaxies in deep Chandra surveys, and the statistical constraints that may be placed on individually undetected populations such as elliptical galaxies at z ≈ 1 2. The data show that there is no overlap between sources discovered in deep submillimeter surveys and those discovered in deep (≈221 ks) X-ray surveys, providing a constraint on the fraction of the submillimeter background produced by star formation. Additional constraints on starbursts detected at radio and mid-infrared wavelengths are also presented. The majority of this thesis focuses on X-ray studies of normal and starburst galaxies using the full 1 million second CDF-N dataset. Statistical methods are used to study field spiral galaxies within the CDF-N in the interval 0.4 < z < 1.5; this investigation reveals that there has not been the strong upwards evolution in X-ray luminosity predicted by some models of X-ray binary production in response to the changing cosmic star formation rate. The level at which normal galaxies should dominate the 0.5 2 keV number counts is determined, and for the first time the number counts of X-ray detected normal galaxies are directly determined. Analysis with the full 1 million second dataset demonstrates that the X-ray detected galaxies within the CDF-N sample are on average more X-ray luminous than truly “normal” galaxies. At these X-ray limits, Chandra is detecting starburst galaxies and lower luminosity AGN in greater numbers than truly quiescent galaxies. Most normal galaxies are detected out to z ≈ 0.15 and some out to z ≈ 0.3. Several instances of off-nuclear ultra-luminous X-ray (ULX) sources within the OBX population, including one extremely notable source which exhibits dramatic grand- design spiral morphology and strong variability in the X- ray band, are also described.
- Publication:
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Ph.D. Thesis
- Pub Date:
- November 2002
- Bibcode:
- 2002PhDT........18H
- Keywords:
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- Physics: Astronomy and Astrophysics