The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos

Abstract

We present the results of the "Cosmogrid" cosmological N-body simulation suites based on the concordance LCDM model. The Cosmogrid simulation was performed in a 30 Mpc box with 2048 3 particles. The mass of each particle is 1.28 × 10 5 M , which is sufficient to resolve ultra-faint dwarfs. We found that the halo mass function shows good agreement with the Sheth & Tormen fitting function down to ∼10 7 M . We have analyzed the spherically averaged density profiles of the three most massive halos which are of galaxy group size and contain at least 170 million particles. The slopes of these density profiles become shallower than −1 at the innermost radius. We also find a clear correlation of halo concentration with mass. The mass dependence of the concentration parameter cannot be expressed by a single power law, however a simple model based on the Press-Schechter theory proposed by Navarro et al. gives reasonable agreement with this dependence. The spin parameter does not show a correlation with the halo mass. The probability distribution functions for both concentration and spin are well fitted by the log-normal distribution for halos with the masses larger than ∼10 8 M . The subhalo abundance depends on the halo mass. Galaxy-sized halos have 50% more subhalos than ∼10 11 M halos have.

Early flattening of dark matter cusps in dwarf spheroidal galaxies

“…Given a halo mass and redshift, the concentration c 200 can be estimated from cosmological N-body simulations (e.g. Muñoz-Cuartas et al 2011;Prada et al 2012;Ogiya et al 2014;Ishiyama et al 2013). For our reference halo model we fix z = 2, M DM = 10 9 M ⊙ , c 200 = 5.69, so the virial radius is r 200 ≃ 10.3 kpc and the scale radius is r s ≃ 1.81 kpc.…”

High Angular Momentum Halo Gas: A Feedback and Code-independent Prediction of LCDM

“…Under this picture of galaxy growth, it is expected that the resulting angular momentum distribution of galaxies should mimic the spin of their dark matter, resulting in rotationally supported galaxy disks (and presumably hot gaseous halos as well) that are proportional to the spin of the dark matter halo (Fall & Efstathiou 1980;Mo et al 1998), which has been well-studied in dissipationless N-body simulations and semi-analytic merger trees (e.g., Bullock et al 2001;Vitvitska et al 2002;Avila-Reese et al 2005;D'Onghia & Navarro 2007;Bett et al 2010;Muñoz-Cuartas et al 2011;Ishiyama et al 2013;Trowland et al 2013;Kim et al 2015).…”

Gas Accretion and Angular Momentum

“…For comparison, examples of best-fit parameters to this lognormal distribution from Bullock et al (2001); Bett et al (2007); Knebe & Power (2008); Ishiyama et al (2013) and Zjupa & Springel (2016) 2 , across a wide range in dark matter halo masses, are shown in Figure 1, showing remarkable agreement among simulations. The mass distributions of angular momentum within dark matter halos has also been shown to fit a universal two-parameter angular momentum profile (Bullock et al, 2001), based on the halo spin parameter as well as a halo shape parameter, though the underlying reason dark matter halos should be fit to a nearly universal angular momentum distribution profile is still not well understood.…”

“…Conserving angular momentum, the galaxy that ultimately forms should also have specific angular momentum similar to that of the dark matter halo, resulting in a rotationally supported disk galaxy (in many cases) with a spin proportional to the dark matter halo (Mestel, 1963;Fall & Efstathiou, 1980;Mo et al, 1998), the statistical properties of which have been well-studied via dissipationless cosmological N-body simulations (e.g. Bullock et al, 2001;Vitvitska et al, 2002;Avila-Reese et al, 2005;D'Onghia & Navarro, 2007;Bett et al, 2010;Muñoz-Cuartas et al, 2011;Ishiyama et al, 2013;Trowland et al, 2013;Kim et al, 2015;Zjupa & Springel, 2016).…”