The APOSTLE simulations: solutions to the Local Group's cosmic puzzles

Abstract

The Local Group of galaxies offer some of the most discriminating tests of models of cosmic structure formation. For example, observations of the Milky Way (MW) and Andromeda satellite populations appear to be in disagreement with N-body simulations of the "Lambda Cold Dark Matter" (ΛCDM) model: there are far fewer satellite galaxies than substructures in cold dark matter halos (the "missing satellites" problem); dwarf galaxies seem to avoid the most massive substructures (the "too-big-tofail" problem); and the brightest satellites appear to orbit their host galaxies on a thin plane (the "planes of satellites" problem). Here we present results from Apostle (A Project Of Simulating The Local Environment), a suite of cosmological hydrodynamic simulations of twelve volumes selected to match the kinematics of the Local Group (LG) members. Applying the Eagle code to the LG environment, we find that our simulations match the observed abundance of LG galaxies, including the satellite galaxies of the MW and Andromeda. Due to changes to the structure of halos and the evolution in the LG environment, the simulations reproduce the observed relation between stellar mass and velocity dispersion of individual dwarf spheroidal galaxies without necessitating the formation of cores in their dark matter profiles. Satellite systems form with a range of spatial anisotropies, including one similar to that of the MW, confirming that such a configuration is not unexpected in ΛCDM. Finally, based on the observed velocity dispersion, size, and stellar mass, we provide new estimates of the maximum circular velocity for the halos of nine MW dwarf spheroidals.

NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes

“…1), indicating a slowing down of the mass accretion histories of the hydro haloes. Similar results have been found in the APOSTLE simulations of Local Group analogues by Sawala et al (2016).…”

Tidal features of classical Milky Way satellites in a Λ cold dark matter universe

“…For details we refer the readers to the original simulation papers Sawala et al 2016). Here we briefly describe some basic properties of the simulations.…”

“…The Eagle code is a modified version of P-Gadget-3, which is an improved version of the publicly available Gadget-2 code (Springel 2005). For our study, we utilize both the medium-resolution (MR) and high-resolution (HR) runs of the APOSTLE simulations (corresponding to L2 and L1 resolution in Sawala et al (2016)). The HR runs consist of three Local Group realizations (AP-1, AP-4, and AP-11 in Fattahi et al (2016)), which contain six MW-mass host haloes with M200 = 1.66×10 12 M⊙, 1.10×10 12 M⊙, 1.38×10 12 M⊙, 1.35 × 10 12 M⊙, 0.99 × 10 12 M⊙, and 0.80 × 10 12 M⊙ at z = 0.…”

“…Models of galaxy formation in a ΛCDM cosmogony can only reproduce the present-day properties of the MW satellite system if a fraction of satellites experience significant mass loss as the result of tidal interactions with their host (Li et al 2010;Barber et al 2015;Sawala et al 2016). Tidal stirring may also be an effective mechanism for transforming disky field dwarfs into objects with properties resembling dSphs (Tomozeiu et al 2016).…”

Evolution of Dwarf Spheroidal Satellites in the Common Surface-Density Dark Halos

“…One is to modify the standard theory of dark matter on small scales, such as theories based on warm or self-interacting dark matter (e.g., Macciò & Fontanot 2010;Lovell et al 2012;Vogelsberger et al 2012). Another way to solve the issues is to rely on the role of baryonic physics in the formation of galaxies and their satellites, including the suppression effects of the ionizing UV background and stellar feedback such as supernova explosion on galaxy formation and tidal effects of a centrally concentrated host galaxy on its satellites (e.g., Di Cintio et al 2014;Madau et al 2014;Pawlowski et al 2015;Sawala et al 2016;Zhu et al 2016).…”