Local Group Analogs in $\Lambda$CDM cosmological simulations

Abstract

We use semi-analytic galaxy catalogs based on two high-resolution cosmological $N$-body simulations, Millennium-WMAP7 and Millennium-II, to investigate the formation of the Local Group (LG) analogs. Unlike previous studies, we use the observed stellar masses to select the LG member (Milky Way (MW) and M31) analogs, and then impose constrains using the observed separation, isolation, and kinematics of the two main member galaxies. By comparing radial and low-ellipticity orbits between the MW and M31, we find higher tangential velocity results in higher total mass, which are 4.4${}_{-1.5}^{+2.4}\times$10${}^{12}{\mathrm{M}}_{\odot }$ and 6.6${}_{-1.5}^{+2.7}\times$10${}^{12}{\mathrm{M}}_{\odot }$ for radial and low-ellipticity orbits. The orbits also influence the individual mass distribution of MW and M31 analogs. For radial orbits, the typical host halo masses of the MW and M31 are 1.5${}_{-0.7}^{+1.4}\times$10${}^{12}{\mathrm{M}}_{\odot }$ and 2.5${}_{-1.1}^{+1.3}\times$10${}^{12}{\mathrm{M}}_{\odot }$; for low-ellipticity orbits, the masses are 2.5${}_{-1.4}^{+2.2}\times$10${}^{12}{\mathrm{M}}_{\odot }$ and 3.8${}_{-1.8}^{+2.8}\times$10${}^{12}{\mathrm{M}}_{\odot }$. The LG is located primarily in filaments with tails extending toward higher densities up to $\delta \sim 4.5$. The dark matter velocity anisotropy parameters $\beta$ of both the MW and M31 analogs are close to zero in the center, increasing to 0.2--0.3 at 50--80 kpc and decreasing slowly outward. The slope is much flatter than computed from the MW satellites, and the amplitude is smaller than traced by halo stars. Values of $\beta$ from different tracers agree at $\sim$120 kpc where $\beta \sim$ 0.2. We also find that model predictions agree broadly with observations in the radial distribution and luminosity function of satellites around the MW and M31.

ApJ accepted

References in corpus (16)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data
• Too big to fail? The puzzling darkness of massive Milky Way subhaloes
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• Bent by baryons: the low mass galaxy-halo relation
• The M31 Velocity Vector. I. Hubble Space Telescope Proper Motion Measurements
• Shaken and Stirred: The Milky Way's Dark Substructures
• A dynamical model of the local cosmic expansion
• Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos
• Discs of Satellites: the new dwarf spheroidals
• Three-dimensional Multi-probe Analysis of the Galaxy Cluster A1689
• Subhalo statistics of galactic halos: beyond the resolution limit
• The Lopsidedness of Satellite Galaxy Systems in $\Lambda$CDM simulations
• Constraining the mass of the Local Group