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Markov Chain Monte Carlo methods applied to measuring the fine structure constant from quasar spectroscopy

Published online by Cambridge University Press:  21 October 2010

Julian King ,
Daniel Mortlock ,
John Webb  and
Michael Murphy
Julian King
Affiliation:
Department of Astronomy, University of New South Wales, Sydney, New South Wales, 2052, Australia email: jking.phys@gmail.com
Daniel Mortlock
Affiliation:
Astrophysics Group, Blackett Laboratory, Prince Consort Road, Imperial College London, London SW7 2AZ, U.K.
John Webb
Affiliation:
Department of Astronomy, University of New South Wales, Sydney, New South Wales, 2052, Australia email: jking.phys@gmail.com
Michael Murphy
Affiliation:
Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Victoria, 3122, Australia
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Abstract

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Recent attempts to constrain cosmological variation in the fine structure constant, α, using quasar absorption lines have yielded two statistical samples which initially appear to be inconsistent. One of these samples was subsequently demonstrated to not pass consistency tests; it appears that the optimisation algorithm used to fit the model to the spectra failed. Nevertheless, the results of the other hinge on the robustness of the spectral fitting program VPFIT, which has been tested through simulation but not through direct exploration of the likelihood function. We present the application of Markov Chain Monte Carlo (MCMC) methods to this problem, and demonstrate that VPFIT produces similar values and uncertainties for Δα/α, the fractional change in the fine structure constant, as our MCMC algorithm, and thus that VPFIT is reliable.

Keywords

Atomic processes – Methods: numerical – Methods: statistical – Quasars: absorption lines – Quasars: individual: LBQS 2206-1958 – Quasars: individual: LBQS 0013-0029 – Quasars: individual: Q 0551-366 – Cosmology: observations
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Highlights H15: Highlights of Astronomy , November 2009 , pp. 318
Copyright
Copyright © International Astronomical Union 2010

References

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