25 research outputs found
The Dark Matter Density in the Solar Neighborhood reconsidered
Both the gas flaring and the dip in the rotation curve, which was recently
reconfirmed with precise measurements using the VERA VLBI array in Japan,
suggest doughnut-like substructure in the dark matter (DM) halo. A global fit
to all available data shows that the data are indeed best described by an NFW
DM profile complemented by two doughnut-like DM substructures with radii of 4.2
and 12.4 kpc, which coincide with the local dust ring and the Monocerus ring of
stars, respectively. Both regions have been suggested as regions with tidal
streams from "shredded" satellites. If real, the radial extensions of these
nearby ringlike structures enhance the local dark matter density by a factor of
four to about 1.3 GeV/cm.
It is shown that i) this higher DM density is perfectly consistent with the
local gravitational potential determining the surface density and the local
matter density (Oort limit), ii) previous determinations of the surface density
were biased by the assumption of a smoothly varying DM halo and iii) the
s-shaped gas flaring is explained. Such a possible enhancement of the local DM
density is of great interest for direct DM searches and would change the
directional dependence for indirect DM searches.Comment: 14 pages, 4 figures, extended version, accepted for publication in
JCA
Structure, mass and stability of galactic disks
In this review I concentrate on three areas related to structure of disks in
spiral galaxies. First I will review the work on structure, kinematics and
dynamics of stellar disks. Next I will review the progress in the area of
flaring of HI layers. These subjects are relevant for the presence of dark
matter and lead to the conclusion that disk are in general not `maximal', have
lower M/L ratios than previously suspected and are locally stable w.r.t.
Toomre's Q criterion for local stability. I will end with a few words on
`truncations' in stellar disks.Comment: Invited review at "Galaxies and their Masks" for Ken Freeman's 70-th
birthday, Sossusvlei, Namibia, April 2010. A version with high-res. figures
is available at
http://www.astro.rug.nl/~vdkruit/jea3/homepage/Namibiachapter.pd