Comprehensive assessment of the too big to fail problem
Abstract
We use a semianalytical model for the substructure of dark matter haloes to assess the too big to fail (TBTF) problem. The model accurately reproduces the average subhalo mass and velocity functions, as well as their halotohalo variance, in Nbody simulations. We construct thousands of realizations of Milky Way (MW)size host haloes, allowing us to investigate the TBTF problem with unprecedented statistical power. We examine the dependence on host halo mass and cosmology, and explicitly demonstrate that a reliable assessment of TBTF requires large samples of hundreds of host haloes. We argue that previous statistics used to address TBTF suffer from the lookelsewhere effect and/or disregard certain aspects of the data on the MW satellite population. We devise a new statistic that is not hampered by these shortcomings, and, using only data on the nine known MW satellite galaxies with V_{max} > 15 km s^{1}, demonstrate that 1.4^{+3.3}_{1.1} per cent of MWsize host haloes have a subhalo population in statistical agreement with that of the MW. However, when using data on the MW satellite galaxies down to V_{max} = 8 km s^{1}, this MW consistent fraction plummets to <5 × 10^{4} (at 68 per cent confidence level). Hence, if it turns out that the inventory of MW satellite galaxies is complete down to 8 km s^{1}, then the maximum circular velocities of MW satellites are utterly inconsistent with Λ cold dark matter predictions, unless baryonic effects can drastically increase the spread in V_{max} values of satellite galaxies compared to that of their subhaloes.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2015
 DOI:
 10.1093/mnras/stv1871
 arXiv:
 arXiv:1508.02715
 Bibcode:
 2015MNRAS.453.3575J
 Keywords:

 methods: analytical;
 methods: statistical;
 Galaxy: halo;
 galaxies: haloes;
 dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 19 pages, 10 figures, accepted for publication in MNRAS