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Can we measure the slopes of density profiles in dwarf spheroidal galaxies? | | Klaudia Kowalczyk
; Ewa L. Lokas
; Stelios Kazantzidis
; Lucio Mayer
; | | Date: |
14 Dec 2012 | | Abstract: | Using collisionless N-body simulations of dwarf galaxies orbiting the Milky
Way (MW) we construct realistic models of dwarf spheroidal (dSph) galaxies of
the Local Group. The dwarfs are initially composed of stellar disks embedded in
dark matter haloes with different inner density slopes and are placed on an
eccentric orbit typical for MW subhaloes. After a few Gyr of evolution the
stellar component is triaxial as a result of bar instability induced by tidal
forces. Observing the simulated dwarfs along three principal axes of the
stellar component we create mock data sets and determine the their half-light
radii and line-of-sight velocity dispersions. Using the estimator proposed by
Wolf et al. we calculate masses within half-light radii. The masses obtained
this way are over(under)estimated by up to a factor of two when the line of
sight is along the longest (shortest) axis of the stellar component. We then
divide the initial stellar distribution into an inner and outer population and
trace their evolution in time. The two populations, although affected by tidal
forces, retain different density profiles even after a few Gyr. We measure the
half-light radii and velocity dispersions of the stars in the two populations
along different lines of sight and use them to estimate the slope of the mass
distribution in the dwarfs following the method proposed by Walker &
Penarrubia. The inferred slopes are systematically over- or underestimated,
depending on the line of sight. In particular, when the dwarf is seen along the
longest axis of the stellar component, a significantly shallower density
profile is inferred than the real one measured from the simulations. Since most
dSphs are non-spherical and their orientation with respect to our line of sight
is unknown, the method can be reliably applied only to a large sample of dwarfs
when these systematic errors are expected to be diminished. | | Source: | arXiv, 1212.3438 | | Services: | Forum | Review | PDF | Favorites | |
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