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The case for a cold dark matter cusp in Draco

Read, J I, Walker, M G and Steger, P (2018) The case for a cold dark matter cusp in Draco Monthly Notices of the Royal Astronomical Society, 481 (1). pp. 860-877.

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Abstract

We use a new mass modelling method, GRAVSPHERE, to measure the central dark matter density profile of the Draco dwarf spheroidal galaxy. Draco's star formation shut down long ago, making it a prime candidate for hosting a `pristine' dark matter cusp, unaffected by stellar feedback during galaxy formation. We first test GRAVSPHERE on a suite of tidally stripped mock `Draco'-like dwarfs. We show that we are able to correctly infer the dark matter density profile of both cusped and cored mocks within our 95 per cent confidence intervals. While we obtain only a weak inference on the logarithmic slope of these density profiles, we are able to obtain a robust inference of the amplitude of the inner dark matter density at 150 pc, ρ _DM(150 pc). We show that, combined with constraints on the density profile at larger radii, this is sufficient to distinguish a Λ Cold Dark Matter (ΛCDM) cusp - that has ρ _DM(150 pc) ≳ 1.8 × 10^8 M_☉ kpc^{-3} - from alternative dark matter models that have lower inner densities. We then apply GRAVSPHERE to the real Draco data. We find that Draco has an inner dark matter density of ρ _DM(150 pc) = 2.4_{-0.6}^{+0.5} × 10^8 M_☉ kpc^{-3}, consistent with a ΛCDM cusp. Using a velocity-independent SIDM model, calibrated on ΛSIDM cosmological simulations, we show that Draco's high central density gives an upper bound on the SIDM cross-section of σ/m < 0.57 cm2 g-1 at 99 per cent confidence. We conclude that the inner density of nearby dwarf galaxies like Draco provides a new and competitive probe of dark matter models.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
NameEmailORCID
Read, J Ij.read@surrey.ac.uk
Walker, M G
Steger, P
Date : 29 August 2018
Funders : Science and Technology Facilities Council (STFC)
DOI : 10.1093/mnras/sty2286
Copyright Disclaimer : © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record J I Read, M G Walker, P Steger; The case for a cold dark matter cusp in Draco, Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 1, 21 November 2018, Pages 860–877, https://doi.org/10.1093/mnras/sty2286 is available online at: https://academic.oup.com/mnras/article/481/1/860/5086082 .
Uncontrolled Keywords : Galaxies: dwarf; Galaxies: haloes; Galaxies: kinematics dynamics; Dark matter; Cosmology: observations; Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics
Depositing User : Clive Harris
Date Deposited : 20 Sep 2018 14:57
Last Modified : 06 Jul 2019 05:26
URI: http://epubs.surrey.ac.uk/id/eprint/849381

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