1,391 research outputs found
Measuring the local dark matter density
We examine systematic problems in determining the local matter density from
the vertical motion of stars, i.e. the 'Oort limit'. Using collisionless
simulations and a Monte Carlo Markov Chain technique, we determine the data
quality required to detect local dark matter at its expected density. We find
that systematic errors are more important than observational errors and apply
our technique to Hipparcos data to reassign realistic error bars to the local
dark matter density.Comment: 3 pages, 1 figure, to be published in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista & C.C. Popescu, AIP Conf. Se
Galactic fountains and gas accretion
Star-forming disc galaxies such as the Milky Way need to accrete \gsim 1
of gas each year to sustain their star formation. This gas
accretion is likely to come from the cooling of the hot corona, however it is
still not clear how this process can take place. We present simulations
supporting the idea that this cooling and the subsequent accretion are caused
by the passage of cold galactic-fountain clouds through the hot corona. The
Kelvin-Helmholtz instability strips gas from these clouds and the stripped gas
causes coronal gas to condense in the cloud's wake. For likely parameters of
the Galactic corona and of typical fountain clouds we obtain a global accretion
rate of the order of that required to feed the star formation.Comment: 2 pages, 1 figure, to appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Se
Are stellar over-densities in dwarf galaxies the "smoking gun" of triaxial dark matter haloes?
We use N-body simulations to study the tidal evolution of globular clusters
(GCs) in dwarf spheroidal (dSph) galaxies. Our models adopt a cosmologically
motivated scenario in which the dSph is approximated by a static NFW halo with
a triaxial shape. For a large set of orbits and projection angles we examine
the spatial and velocity distribution of stellar debris deposited during the
complete disruption of stellar clusters. Our simulations show that such debris
appears as shells, isolated clumps and elongated over-densities at low surface
brightness (>26 mag/arcsec^2), reminiscent of substructure observed in several
MW dSphs. Such features arise from the triaxiality of the galaxy potential and
do not dissolve in time. Stellar over-densities reported in several MW dSphs
may thus be the telltale evidence of dark matter haloes being triaxial in
shape.
We explore a number of kinematic signatures that would help to validate (or
falsify) this scenario. The mean angular momentum of the cluster debris
associated with box and resonant orbits, which are absent in spherical
potentials, is null. As a result, we show that the line-of-sight velocity
distribution may exhibit a characteristic "double-peak" depending on the
oriention of the viewing angle with respect to the progenitor's orbital plane.
Kinematic surveys of dSphs may help to detect and identify substructures
associated with the disruption of stellar clusters, as well as to address the
shape of the dark matter haloes in which dSphs are embedded.Comment: 4 pages, 2 figures, to be published in the proceedings of "Hunting
for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009,
eds. V.P. Debattista & C.C. Popescu, AIP Conf. Ser., in pres
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