Dark matter density profiles of the halos embedding early-type galaxies: characterizing halo contraction and dark matter annihilation strength

Details Dark matter density profiles of the halos embedding early-type galaxies: characterizing halo contraction and dark matter annihilation strength Dark matter density profiles of the halos embedding early-type galaxies: characterizing halo contraction and dark matter annihilation strength

2012-02-13

arxiv.org/abs/1202.2716v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

33 pages, 17 figures, JCAP, submitted

Scientific paper

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.

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