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Dwarf spheroidal J-factors without priors: A likelihood-based analysis for indirect dark matter searches
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
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Number of Authors: 62017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 466, no 1, p. 669-676Article in journal (Refereed) Published
Abstract [en]

Line-of-sight integrals of the squared density, commonly called the J-factor, are essential for inferring dark matter (DM) annihilation signals. The J-factors of DM-dominated dwarf spheroidal satellite galaxies (dSphs) have typically been derived using Bayesian techniques, which for small data samples implies that a choice of priors constitutes a non-negligible systematic uncertainty. Here we report the development of a new fully frequentist approach to construct the profile likelihood of the J-factor. Using stellar kinematic data from several classical and ultra-faint dSphs, we derive the maximum likelihood value for the J-factor and its confidence intervals. We validate this method, in particular its bias and coverage, using simulated data from the Gaia Challenge. We find that the method possesses good statistical properties. The J-factors and their uncertainties are generally in good agreement with the Bayesian-derived values, with the largest deviations restricted to the systems with the smallest kinematic data sets. We discuss improvements, extensions, and future applications of this technique.

Place, publisher, year, edition, pages
2017. Vol. 466, no 1, p. 669-676
Keywords [en]
galaxies: dwarf, galaxies: kinematics and dynamics, dark matter
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-142610DOI: 10.1093/mnras/stw3079ISI: 000398112400046OAI: oai:DiVA.org:su-142610DiVA, id: diva2:1097288
Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2019-01-29Bibliographically approved
In thesis
1. Dark matter signal normalisation for dwarf spheroidal galaxies: A frequentist analysis of stellar kinematics for indirect Dark Matter searches
Open this publication in new window or tab >>Dark matter signal normalisation for dwarf spheroidal galaxies: A frequentist analysis of stellar kinematics for indirect Dark Matter searches
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Indirect detection strategies of Dark Matter (DM) entail searching for signals of DM annihilation or decay, typically in the form of excess positrons or high-energy photons above the astrophysical background, originating from (inferred) DM-rich environments. Due to their characteristics, dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are considered very promising targets for indirect particle DM identification. To compare model predictions with the observed fluxes of product particles, most analyses of astrophysical data - which are generally performed via frequentist statistics - rely on estimating the abundance of DM by calculating the so-called J-factor. This quantity is usually inferred from the kinematic properties of the stellar population of a dSph, performing a Jeans analysis by means of Bayesian techniques. Previous works have, therefore, combined different statistical methods when analysing astrophysical data from dSphs. This thesis describes the development of a new, fully frequentist approach for constructing the profile likelihood curve for J-factors of dSphs, which can be implemented in indirect DM searches. This method improves upon previous ones by producing data-driven expressions of the likelihood of J, thereby allowing a statistically consistent treatment of the astroparticle and astrometric data from dSphs. Using kinematic data from twenty one satellites of the Milky Way, we derive estimates of their maximum likelihood J-factor and its confidence intervals. The analyses are performed in two different frameworks: the standard scenario of a collisionless DM candidate and the possibility of a self-interacting DM species. In the former case, the obtained J-factors and their uncertainties are consistent with previous, Bayesian-derived values. In the latter, we present prior-less estimates for the Sommerfeld enhanced J-factor of dSphs. In agreement with earlier studies, we find J to be overestimated by several orders of magnitude when DM is allowed is attractively self-interact. In both cases we provide the profile likelihood curves obtained. This technique is validated on a publicly available simulation suite, released by Gaia Challenge, by evaluating its coverage and bias. The results of these tests indicate that the method possesses good statistical properties. Lastly, we discuss the implications of these findings for DM searches, together with future improvements and extensions of this technique.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2019. p. 131
Keywords
dark matter, dwarf galaxies, kinematics and dynamics of galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-165273 (URN)978-91-7797-560-1 (ISBN)978-91-7797-561-8 (ISBN)
Public defence
2019-03-13, FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
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Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2019-02-18 Created: 2019-01-23 Last updated: 2019-02-08Bibliographically approved

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