Mass modelling of dwarf spheroidal galaxies: the effect of unbound stars from tidal tails and the Milky Way

被引:88
作者
Klimentowski, Jaroslaw
Lokas, Ewa L.
Kazantzidis, Stelios
Prada, Francisco
Mayer, Lucio
Mamon, Gary A.
机构
[1] Nicolaus Copernicus Astron Ctr, PL-00716 Warsaw, Poland
[2] Stanford Univ, Dept Phys, Kavli Inst Particle Astrophys & Cosmol, Stanford, CA 94309 USA
[3] CSIC, Inst Astrofis Andulucia, E-18080 Granada, Spain
[4] Univ Zurich, Inst Theoret Phys, CH-8057 Zurich, Switzerland
[5] Swiss Fed Inst Technol, Dept Phys, Inst Astron, CH-8093 Zurich, Switzerland
[6] CNRS, UMR 7095, Inst Astrophys Paris, F-75014 Paris, France
[7] Univ Paris 06, F-75014 Paris, France
[8] CNRS, UMR 8111, GEPI, F-92195 Meudon, France
[9] Univ Paris 07, Observ Paris, F-92195 Meudon, France
关键词
galaxies : clusters : individual : fornax; galaxies : dwarf; galaxies : fundamental parameters; galaxies : kinematics and dynamics; local group; dark matter;
D O I
10.1111/j.1365-2966.2007.11799.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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.
引用
收藏
页码:353 / 368
页数:16
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