Statistics of Dark Matter Substructure: III. Halo-to-Halo Variance

Understand

We present a study of unprecedented statistical power regarding the halo-to-halo variance of dark matter substructure.

• Using a combination of N-body simulations and a semi-analytical model, we investigate the variance in subhalo mass fractions and subhalo occupation numbers, with an emphasis on how these statistics scale with halo formation time.
• We demonstrate that the subhalo mass fraction, f_sub, is mainly a function of halo formation time, with earlier forming haloes having less substructure.
• At fixed formation redshift, the average f_sub is virtually independent of halo mass, and the mass dependence of f_sub is therefore mainly a manifestation of more massive haloes assembling later.