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Title: Solving the catalogue cross-match problem in the Galactic plane
Author: Wilson, Thomas Jareth
ISNI:       0000 0004 7232 1639
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2018
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In this thesis the cross-matching problem is considered. One of the most fundamental processes in astrophysics, the cross-matching of two photometric catalogues is the assignment of an object in one catalogue and one object from the second catalogue as pairs, i.e., different detections of the same physical source in the sky. I present here new methods for considering such a problem, including the additional magnitude information available in photometric catalogues to break degeneracies between astrometric matches. I also generalise the Astrometric Uncertainty Function (AUF), usually assumed to be a Gaussian, to allow for the inclusion of systematic astrometric perturbations, such as those from blended sources of contamination. The separations of sources in several widely used photometric catalogues with respect to the much more precise Gaia positions are considered. I find that the separations are described by a combination of a Gaussian distribution and a large non-Gaussian wing, and show that this is caused by flux contamination from blended stars not treated separately. At least one in three of the stars in the faint half of a given catalogue will suffer from flux contamination above the 1% level when the density of catalogue objects per point-spread function area is above approximately 0.005. I then introduce a new method to use the additional photometric information from both catalogues in the process of accepting or rejecting counterparts, providing approximately a factor 10 improvement in Bayes' factor with its inclusion. The method uniquely combines photometric information from both catalogues while avoiding the use of prior astrophysical knowledge. Additionally, I formally describe the probability of two sources being the same astrometric object, allowing systematic effects of astrometric perturbation (by, e.g., contaminant objects) to be accounted for. I apply this method to two key match cases, of two catalogues of similar wavelength coverage but differing dynamic ranges, and of two catalogues with approximately equal astrometric precision, discussing the importance of the inclusion of the magnitude information in each case. Finally, the extension to the inclusion of perturbations due to faint contaminant stars in the AUFs of catalogues is combined with the improved cross-matching method for the specific case of the Wide-field Infrared Survey Explorer (WISE) catalogue. I describe the rigorous construction of the description of astrometric offsets due to faint stars, and then apply the method to Gaia-WISE matches in the Galactic plane. I analyse several test cases and discuss the photometric effects of the blended star contamination, showing that stars with significant astrometric perturbation are detectably photometrically compromised. I discuss the implications this has on derived parameters in several areas of astrophysics.
Supervisor: Naylor, Tim ; Hatchell, Jennifer Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available