A Two Micron All‐Sky Survey View of the Sagittarius Dwarf Galaxy. IV. Modeling the Sagittarius Tidal Tails

Abstract

M giants recovered from the Two Micron All-Sky Survey (2MASS) have recently\nbeen used to map the position and velocity distributions of tidal debris from\nthe Sagittarius (Sgr) dwarf spheroidal galaxy entirely around the Galaxy. We\ncompare this data set to both test particle orbits and N-body simulations of\nsatellite destruction run within a variety of rigid Milky Way potentials and\nfind that the mass of the Milky Way within 50 kpc of its center should be\n3.8-5.6 x 10^11 Msun in order for any Sgr orbit to simultaneously fit the\nvelocity gradient in the Sgr trailing debris and the apocenter of the Sgr\nleading debris. Orbital pole precession of young debris and leading debris\nvelocities in regions corresponding to older debris provide contradictory\nevidence in favor of oblate/prolate Galactic halo potentials respectively,\nleading us to conclude that the orbit of Sgr has evolved over the past few Gyr.\n Based upon the velocity dispersion and width along the trailing tidal stream\nwe estimate the current bound mass of Sgr to be M_Sgr = 2 - 5 x 10^8 Msun\nindependant of the form of the Galactic potential; this corresponds to a range\nof mass to light ratios (M/L)_Sgr = 14 - 36 (M/L)_Sun for the Sgr core. Models\nwith masses in this range best fit the apocenter of leading Sgr tidal debris\nwhen they orbit with a radial period of roughly 0.85 Gyr and have periGalactica\nand apoGalactica of about 15 kpc and 60 kpc respectively. These distances will\nscale with the assumed distance to the Sgr dwarf and the assumed depth of the\nGalactic potential. The density distribution of debris along the orbit in these\nmodels is consistent with the M giant observations, and debris at all orbital\nphases where M giants are obviously present is younger (i.e. was lost more\nrecently from the satellite) than the typical age of a Sgr M giant star.\n