[en] What was the mass of the progenitor of the Sagittarius (Sgr) dwarf galaxy? Here, we reassemble the stellar debris using Sloan Digital Sky Survey and Two Micron All-Sky Survey data to find the total luminosity and likely mass. We find that the luminosity is in the range (9.6-13.2) x 10⁷ L_sun or M_V ∼ -15.1 to -15.5, with 70% of the light residing in the debris streams. The progenitor is somewhat fainter than the present-day Small Magellanic Cloud, and comparable in brightness to the M31 dwarf spheroidals NGC 147 and NGC 185. Using cosmologically motivated models, we estimate that the mass of Sgr's dark matter halo prior to tidal disruption was ∼10¹⁰ M_sun.

[en] We report the detection of a pair of degree-long tidal tails associated with the globular cluster Palomar 14, using images obtained at the Canada-France-Hawaii Telescope. We reveal a power-law departure from a King profile at large distances to the cluster center. The density map constructed with the optimal matched filter technique shows a nearly symmetrical and elongated distribution of stars on both sides of the cluster, forming an S-shape characteristic of mass loss. This evidence may be the telltale signature of tidal stripping in action. This, together with its large Galactocentric distance, imposes strong constraints on its orbit and/or origin: (1) it must follow an external orbit confined to the peripheral region of the Galactic halo and/or (2) it formed in a satellite galaxy later accreted by the Milky Way.

[en] We present the results of deep imaging obtained at the Canada-France-Hawaii Telescope with MegaCam in the anticenter direction at two different heights above the Galactic disk. We detect the presence of the Monoceros ring in both fields as a conspicuous and narrow main-sequence feature which dominates star counts over a large portion of the color-magnitude diagram down to g' ∼ 24. The comparison of the morphology and density of this feature with a large variety of Galactic models excludes the possibility that it can be due to a flare of the Galactic disk, supporting an extra-Galactic origin for this ring-like structure.

[en] We develop, implement, and characterize an enhanced data reduction approach which delivers precise, accurate, radial velocities from moderate resolution spectroscopy with the fiber-fed VLT/FLAMES+GIRAFFE facility. This facility, with appropriate care, delivers radial velocities adequate to resolve the intrinsic velocity dispersions of the very faint dwarf spheroidal (dSph) galaxies. Importantly, repeated measurements let us reliably calibrate our individual velocity errors (0.2 kms^-1 ≤ δ_V ≤ 5 km s^-1) and directly detect stars with variable radial velocities. We show, by application to the Booetes I dSph, that the intrinsic velocity dispersion of this system is significantly below 6.5 km s^-1 reported by previous studies. Our data favor a two-population model of Booetes I, consisting of a majority 'cold' stellar component, with velocity dispersion 2.4^+0.9_-0.5 km s^-1, and a minority 'hot' stellar component, with velocity dispersion ∼9 km s^-1, although we cannot completely rule out a single component distribution with velocity dispersion 4.6^0.8_-0.6 km s^-1. We speculate that this complex velocity distribution actually reflects the distribution of velocity anisotropy in Booetes I, which is a measure of its formation processes.

[en] Wrapping around the Milky Way, the Sagittarius stream is the dominant substructure in the halo. Our statistical selection method has allowed us to identify 106 highly likely members of the Sagittarius stream. Spectroscopic analysis of metallicity and kinematics of all members provides us with a new mapping of the Sagittarius stream. We find correspondence between the velocity distribution of stream stars and those computed for a triaxial model of the Milky Way dark matter halo. The Sagittarius trailing arm exhibits a metallicity gradient, ranging from −0.59 to −0.97 dex over 142°. This is consistent with the scenario of tidal disruption from a progenitor dwarf galaxy that possessed an internal metallicity gradient. We note high metallicity dispersion in the leading arm, causing a lack of detectable gradient and possibly indicating orbital phase mixing. We additionally report on a potential detection of the Sextans dwarf spheroidal in our data