2018-05-04  P7F

Probing physical boundaries of dark matter halos from cosmic density and velocity fields

Teppei OKUMURA

In the current paradigm of cosmic structure formation, galaxies, which are observed as a tracer of the large-scale structure of the universe, are considered to be formed within dark-matter halos. Dark matter halos thus play a fundamental role in both structure formation and cosmological studies. Recently, the phase-space structure in halo outskirts has been extensively studied based on N-body simulations, leading to the discovery of a steepening in the outer density profile of dark-matter halos. This feature is interpreted as a sharp density enhancement associated with the orbital apocenter of the recently accreted matter in the growing halo potential. The location of this steepening is referred to as the splashback radius and depends on cosmology as well as on halo mass and redshift. The splashback radius provides a physical boundary of halos, and is related to the transition scale between the 1-halo and 2-halo regimes in the galaxy power spectrum or correlation function to a certain extent. 

In this talk I will present an analysis of the splashback features of dark-matter halos based on cosmic density and velocity fields. Besides the density correlation function binned by the halo orientation angle which was used in the literature, we introduce, for the first time, the corresponding velocity statistic, alignment momentum correlation function. Using large-volume, high-resolution N-body simulations, we measure the alignment statistics of density and velocity. On halo scales, ∼1 Mpc/h, we detect the splashback feature, which is found more prominent than in the density correlation. We also find that the splashback radius determined from the density correlation becomes ∼ 3.5% smaller that from the momentum correlation, with their correlation coefficient being 0.605. Moreover, the orientation-dependent splashback feature due to halo asphericity is measured when the density profile is determined by dark-matter particles, which can be used as a test of collisional CDM. 

 

  Presentation Slides