A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms

We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy, mapped by M giant star tracers detected in the complete Two Micron All-Sky Survey (2MASS). The Sgr core is fit with a King profile of limiting radius 30 deg but exhibits a prominent break corresponding to the tidal debris, a profile resembling those of other Galactic dSph galaxies. Adopting published central velocity dispersions, we derive a total Sgr M/L of 25 in solar units. A striking, >150 deg trailing Sgr debris arm arcs completely across the Southern Galactic Hemisphere at mean distance 20-40 kpc. The prominent leading debris arm extends north of the Galactic plane to an apoGalacticon ~45 kpc from the Sun, then turns towards the North Galactic Pole from where it descends back towards the Galactic plane, becomes foreshortened and covers the North Galactic Cap. For less than 2% of the solar orbit are we closer to the mid-plane of Sgr debris tails at the Solar Circle. It is likely that leading Sgr tidal debris is in the solar neighborhood. The Sgr orbit shows minimal precession, with tidal debris confined to a coherent planar distribution. The number of M giants in the tidal arms are 15% those in the bound core. Variation of length and density of Sgr tails with M giant colors suggests a possible age/metallicity variation along the arms. Sgr contributes more than 75% of high latitude, halo M giants; no evidence of M giant tidal debris from the Magellanic Clouds is found. The 2MASS map of the Sgr system is compared to all previous identifications of potential Sgr debris. Sgr carbon stars are subluminous with respect to Magellanic Cloud carbon stars, and trace the Sgr system less clearly than M giants, even though Sgr carbon stars account for the majority of the total high latitude Galactic halo carbon star sample