158 research outputs found
A Model for Dark Matter Halos
A halo model is presented which possesses a constant phase space density (Q)
core followed by a radial CDM-like power law decrease in Q. The motivation for
the core is the allowance for a possible primordial phase space density limit
such as the Tremaine-Gunn upper bound. The space density profile derived from
this model has a constant density core and falls off rapidly beyond. The new
model is shown to improve the fits to the observations of LSB galaxy rotation
curves, naturally provides a model which has been shown to result in a
lengthened dynamical friction time scale for the Fornax dwarf spheroidal galaxy
and predicts a flattening of the density profile within the Einstein radius of
galaxy clusters. A constant gas entropy floor is predicted whose adiabatic
constant provides a lower limit in accord with observed galaxy cluster values.
While `observable-sized' cores are not seen in standard cold dark matter (CDM)
simulations, phase space considerations suggest that they could appear in warm
dark matter (WDM) cosmological simulations and in certain hierarchically
consistent SuperWIMP scenarios.Comment: 14 pages, 3 figures, accepted for publication in Ap
Unstable Cold Dark Matter and the Cuspy Halo Problem in Dwarf Galaxies
We speculate that the dark halos of dwarf galaxies and low surface brightness
galaxies soften their central cusps by the decay of a fraction of cold dark
matter (CDM) particles to a stable particle with a recoiling velocity of a few
tens km s, after they have driven the formation of galactic halos. This
process, however, does not necessarily produce a significant reduction of the
central dark matter density of satellite dwarf spheroidals like Draco or
Fornax. It is shown that the recovered distribution of concentration parameters
for the initial (before decay) Navarro-Frenk-White halos, is in good
agreement with CDM predictions. Other interesting potentials of unstable CDM
are highlighted.Comment: 5 pages, 1 figure, accepted for publication in ApJ
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