Kyu-Hyun Chae, Andrey V. Kravtsov, Joshua A. Frieman, Mariangela Bernardi
Identifying dark matter and characterizing its distribution in the inner
region of halos embedding galaxies are inter-related problems of broad
importance. We devise a new procedure of determining dark matter distribution
in halos. We first make a self-consistent bivariate statistical match of
stellar mass and velocity dispersion with halo mass as demonstrated here for
the first time. Then, selecting early-type galaxy-halo systems we perform Jeans
dynamical modeling with the aid of observed statistical properties of stellar
mass profiles and velocity dispersion profiles. Dark matter density profiles
derived specifically using Sloan Digital Sky Survey galaxies and halos from
up-to-date cosmological dissipationless simulations deviate significantly from
the dissipationless profle of Navarro-Frenk-White or Einasto in terms of inner
density slope and/or concentration. From these dark matter profiles we find
that dark matter density is enhanced in the inner region of most early-type
galactic halos providing an independent dynamical evidence for halo
contraction. The main characteristics of halo contraction are: (1) the mean
dark matter density within the effective radius has increased by a factor from
~1 for clusters with M_vir > 10^{15} M_solar to ~4-5 for galaxies with M_vir <
10^{12} M_solar where M_vir is the halo virial mass, and (2) the enhancement is
more frequently realized by steepened density slope than increased
concentration compared with the fiducial NFW profile. Based on our results we
predict that halos of nearby elliptical and lenticular galaxies can be
promising targets for $\gamma$-ray emission from dark matter annihilation.
View original:
http://arxiv.org/abs/1202.2716
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