The MUSE-Faint survey

Astronomy and Astrophysics, vol. 651, pp. A80

Abstract

Aims. We use stellar line-of-sight velocities to constrain the dark-matter density profile of Eridanus 2, an ultra-faint dwarf galaxy with an absolute V -band magnitude M V = −7.1 that corresponds to a stellar mass M * ≈ 9 × 10 4 M ⊙ . We furthermore derive constraints on fundamental properties of self-interacting and fuzzy dark matter scenarios. Methods. We present new observations of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope, and determine line-of-sight velocities for stars inside the half-light radius. Combined with literature data, we have 92 stellar tracers out to twice the half-light radius. With these tracers we constrain models of cold dark matter, self-interacting dark matter, and fuzzy dark matter, using CJAM and pyGravSphere for the dynamical analysis. The models of self-interacting and fuzzy dark matter relate the density profile to the self-interaction coefficient and the dark-matter particle mass, respectively. Results. We find substantial evidence (Bayes factor ∼10 −0.6 ) for cold dark matter (a cuspy halo) over self-interacting dark matter (a cored halo) and weak evidence (Bayes factor ∼10 −0.4 ) for fuzzy dark matter over cold dark matter. We find a virial mass M 200 ∼ 10 8 M ⊙ and astrophysical factors J ( α c J ) ~ 10 11 M ⊙ 2 kpc −5 and D ( α c D ) ~ 10 2 − 10 2.5 M ⊙ kpc −2 (proportional to dark-matter annihilation and decay signals, respectively), the exact values of which depend on the density profile model. The mass-to-light ratio within the half-light radius is consistent with the literature. We do not resolve a core ( r c < 47 pc, 68% confidence level) or a soliton ( r sol < 7.2 pc, 68% confidence level). These limits are equivalent to an effective self-interaction coefficient f Γ < 2.2 × 10 −29 cm 3 s −1 eV −1 c 2 and a fuzzy-dark-matter particle mass m a > 4.0 × 10 −20 eV c −2 . The constraint on self-interaction is complementary to those from gamma-ray searches. The constraint on fuzzy-dark-matter particle mass is inconsistent with those obtained for larger dwarf galaxies, suggesting that the flattened density profiles of those galaxies are not caused by fuzzy dark matter.

Authors 8

1. Sebastiaan L. Zoutendijk Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

2. J. Brinchmann Aachen Leiden Observatory

   Leiden University · Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto · Leiden Observatory

   Affiliation as printed

   Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

3. N. Bouché

   École Normale Supérieure de Lyon · Centre National de la Recherche Scientifique · Centre de Recherche Astrophysique de Lyon

   Affiliation as printed

   Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France

4. Mark den Brok

   Leibniz Institute for Astrophysics Potsdam

   Affiliation as printed

   Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

5. D. Krajnović

   Leibniz Institute for Astrophysics Potsdam

   Affiliation as printed

   Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

6. Konrad H. Kuijken Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

7. Michael V. Maseda Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

8. Joop Schaye Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands