TY - JOUR
T1 - Unbiased constraints on ultralight axion mass from dwarf spheroidal galaxies
AU - González-Morales, Alma X.
AU - Marsh, David J.E.
AU - Peñarrubia, Jorge
AU - Ureña-López, Luis A.
N1 - Publisher Copyright:
© 2018 The Author(s).
Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 2017
Y1 - 2017
N2 - It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with ma ~ 10-22 eV are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here, we use realistic kinematic mock data catalogues of Milky Way (MW) dSph's to show that the 'mass-anisotropy degeneracy' in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components, this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with reported stellar subcomponents, Fornax and Sculptor, and assuming that the halo profile has not been acted on by baryons, yields core radii rc > 1.5 and 1.2 kpc, respectively, and ma < 0.4 × 10-22 eV at 97.5 per cent confidence. These bounds are in tension with the number of observed satellites derived from simple (but conservative) estimates of the subhalo mass function inMW-like galaxies. We discuss howbaryonic feedback might affect our results, and the impact of such a small axion mass on the growth of structures in the Universe.
AB - It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with ma ~ 10-22 eV are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here, we use realistic kinematic mock data catalogues of Milky Way (MW) dSph's to show that the 'mass-anisotropy degeneracy' in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components, this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with reported stellar subcomponents, Fornax and Sculptor, and assuming that the halo profile has not been acted on by baryons, yields core radii rc > 1.5 and 1.2 kpc, respectively, and ma < 0.4 × 10-22 eV at 97.5 per cent confidence. These bounds are in tension with the number of observed satellites derived from simple (but conservative) estimates of the subhalo mass function inMW-like galaxies. We discuss howbaryonic feedback might affect our results, and the impact of such a small axion mass on the growth of structures in the Universe.
KW - Dark matter
KW - Galaxies: dwarf
KW - Gravitation
KW - Local Group
UR - http://www.scopus.com/inward/record.url?scp=85041330488&partnerID=8YFLogxK
U2 - 10.1093/MNRAS/STX1941
DO - 10.1093/MNRAS/STX1941
M3 - Article
AN - SCOPUS:85041330488
SN - 0035-8711
VL - 472
SP - 1346
EP - 1360
JO - MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
JF - MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
IS - 2
ER -