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Title:
Mass modelling of dwarf spheroidal galaxies: the effect of unbound stars from tidal tails and the Milky Way
Authors:
Klimentowski, Jarosław; Łokas, Ewa L.; Kazantzidis, Stelios; Prada, Francisco; Mayer, Lucio; Mamon, Gary A.
Affiliation:
AA(Nicolaus Copernicus Astronomical Centre, Bartycka 18, 00-716 Warsaw, Poland), AB(Nicolaus Copernicus Astronomical Centre, Bartycka 18, 00-716 Warsaw, Poland), AC(Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics, Stanford University, PO Box 20450, M/S 29, Stanford, CA 94309, USA), AD(Instituto de Astrofísica de Andalucia (CSIC), Apartado Correos 3005, E-18080 Granada, Spain), AE(Institute for Theoretical Physics, University of Zürich, CH-8057 Zürich, Switzerland; Institute of Astronomy, Department of Physics, ETH Zürich, Wolfgang-Pauli Strasse, CH-8093 Zürich, Switzerland), AF(Institut d'Astrophysique de Paris (UMR 7095: CNRS and Université Pierre & Marie Curie), 98 bis Bd Arago, F-75014 Paris, France; GEPI (UMR 8111: CNRS and Université Denis Diderot), Observatoire de Paris, F-92195 Meudon, France)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 378, Issue 1, pp. 353-368. (MNRAS Homepage)
Publication Date:
06/2007
Origin:
MNRAS
MNRAS Keywords:
galaxies: clusters: individual: Fornax, galaxies: dwarf, galaxies: fundamental parameters, galaxies: kinematics and dynamics, Local Group, dark matter
DOI:
10.1111/j.1365-2966.2007.11799.x
Bibliographic Code:
2007MNRAS.378..353K

Abstract

We study the origin and properties of the population of unbound stars in the kinematic samples of dwarf spheroidal (dSph) galaxies. For this purpose we have run a high-resolution N-body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. In agreement with the tidal stirring scenario of Mayer et al., the dwarf is placed on a highly eccentric orbit, its initial stellar component is in the form of an exponential disc and it has a NFW-like dark matter (DM) halo. After 10 Gyr of evolution the dwarf produces a spheroidal stellar component and is strongly tidally stripped so that mass follows light and the stars are on almost isotropic orbits. From this final state, we create mock kinematic data sets for 200 stars by observing the dwarf in different directions. We find that when the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. We also study another source of possible contamination by adding stars from the Milky Way. We demonstrate that most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert and recently tested on simulated DM haloes. We model the cleaned-up kinematic samples using solutions of the Jeans equation with constant mass-to-light ratio (M/L) and velocity anisotropy parameter. We show that even for such a strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and M/L of the dwarf with accuracy typically better than 25 per cent and almost exactly in the case when the line of sight is perpendicular to the tidal tails. The analysis was applied to the new data for the Fornax dSph galaxy. We show that after careful removal of interlopers the velocity dispersion profile of Fornax can be reproduced by a model in which mass traces light with a M/L of 11 solar units and isotropic orbits. We demonstrate that most of the contamination in the kinematic sample of Fornax probably originates from the Milky Way.
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