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The parameter space of galaxy formation.

Bower, R. G. and Vernon, I. and Goldstein, M. and Benson, A. J. and Lacey, Cedric G. and Baugh, C. M. and Cole, Shaun and Frenk, C. S. (2010) 'The parameter space of galaxy formation.', Monthly notices of the Royal Astronomical Society., 407 (4). pp. 2017-2045.


Semi-analytic models are a powerful tool for studying the formation of galaxies. However, these models inevitably involve a significant number of poorly constrained parameters that must be adjusted to provide an acceptable match to the observed Universe. In this paper, we set out to quantify the degree to which observational data sets can constrain the model parameters. By revealing degeneracies in the parameter space we can hope to better understand the key physical processes probed by the data. We use novel mathematical techniques to explore the parameter space of the galform semi-analytic model. We base our investigation on the Bower et al. version of galform, adopting the same methodology of selecting model parameters based on an acceptable match to the local bJ and K luminosity functions. Since the galform model is inherently approximate, we explicitly include a model discrepancy term when deciding if a match is acceptable or not. The model contains 16 parameters that are poorly constrained by our prior understanding of the galaxy formation processes and that can plausibly be adjusted between reasonable limits. We investigate this parameter space using the Model Emulator technique, constructing a Bayesian approximation to the galform model that can be rapidly evaluated at any point in parameter space. The emulator returns both an expectation for the galform model and an uncertainty which allows us to eliminate regions of parameter space in which it is implausible that a galform run would match the luminosity function data. By combining successive waves of emulation, we show that only 0.26 per cent of the initial volume is of interest for further exploration. However, within this region we show that the Bower et al. model is only one choice from an extended subspace of model parameters that can provide equally acceptable fits to the luminosity function data. We explore the geometry of this region and begin to explore the physical connections between parameters that are exposed by this analysis. We also consider the impact of adding additional observational data to further constrain the parameter space. We see that the known tensions existing in the Bower et al. model lead to a further reduction in the successful parameter space.

Item Type:Article
Keywords:Galaxies: formation, Galaxies: luminosity function, mass function.
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Publisher statement:This article has been published in the Monthly Notices of the Royal Astronomical Society ©: 2010 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:20 November 2013
Date of first online publication:October 2010
Date first made open access:No date available

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