The Galaxy's Eating Habits

We report on a 60 degree-long stream of stars, extending from Ursa Major to Sextans, in the Sloan Digital Sky Survey. The stream is approximately 2 degrees wide and is clearly distinct from the northern tidal arm of the Sagittarius dwarf galaxy. The apparent width of the stream suggests a progenitor with a size and mass similar to that of a dwarf galaxy. The stream is about 21 kpc distant and appears to be oriented almost perpendicular to our line of sight. The visible portio...

We identify new structures in the halo of the Milky Way Galaxy from positions, colors and magnitudes of five million stars detected in the Sloan Digital Sky Survey. Most of these stars are within 1.26 degrees of the celestial equator. We present color-magnitude diagrams (CMDs) for stars in two previously discovered, tidally disrupted structures. The CMDs and turnoff colors are consistent with those of the Sagittarius dwarf galaxy, as had been predicted. In one direction, we a...

Motivated by recent observations of the Sagittarius stream, we devise a rapid algorithm to generate faithful representations of the centroids of stellar tidal streams formed in a disruption of a progenitor of an arbitrary mass in an arbitrary potential. Our method works by releasing swarms of test particles at the Lagrange points around the satellite and subsequently evolving them in a combined potential of the host and the progenitor. We stress that the action of the progeni...

We use the SDSS/SEGUE spectroscopic sample of stars in the leading and trailing streams of the Sagittarius (Sgr) to demonstrate the existence of two sub-populations with distinct chemistry and kinematics. The metallicity distribution function (MDF) of the trailing stream is decomposed into two Gaussians describing a metal-rich sub-population with means and dispersions (-0.74, 0.18) dex and a metal-poor with (-1.33, 0.27) dex. The metal-rich sub-population has a velocity dispe...

Hydrodynamical calculations undertaken to simulate the collisional interaction between the Sgr dwarf galaxy and the Galactic outer HI disk are presented, constrained by recently derived orbital and mass parameters for this dwarf galaxy. It is found that a significant distortion to the structure of the Galactic HI disk will be induced by the collision if the mass of the dwarf exceeds ~10^9 M_Sun; this value is consistent with an estimate derived by requiring that the dwarf gal...

We have obtained deep photometric data in 24 fields along the southeast extension of the major axis of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy, and in four fields along the northwest extension. Using star counts at the expected position of the Sgr upper main-sequence within the resulting color-magnitude diagrams (CMDs), we unambiguously detect Sgr stars in the southeast over the range 10--34 degreesfrom the galaxy's center. If Sgr is symmetric, this implies a true ...

We present the first detailed quantitative study of the stellar populations of the Sagittarius (Sgr) streams within the Stripe 82 region, using photometric and spectroscopic observations from the Sloan Digital Sky Survey (SDSS). The star formation history (SFH) is determined separately for the bright and faint Sgr streams, to establish whether both components consist of a similar stellar population mix or have a distinct origin. Best fit SFH solutions are characterised by a...

It is a challenge to reproduce the full 6D space-phase properties of Sagittarius (Sgr) dwarf galaxy and its Stream simultaneously. Using N-body simulations with a Milky Way mass of 5.2$\times10^{11}$ M$_{\odot}$ and a ``scaling down'' Sgr mass of 9.3$\times10^{8}$ M$_{\odot}$, from a qualitative point of view, we have been able to reproduce well all 3D spatial features of Sgr stream, including its core, leading and trailing arms, and their associated bifurcations, moreover, t...

The latest Sloan Digital Sky Survey data reveal a prominent bifurcation in the distribution of debris of the Sagittarius dwarf spheroidal (Sgr) beginning at a right ascension of roughly 190 degrees. Two branches of the stream (A and B) persist at roughly the same heliocentric distance over at least 50 degrees of arc. There is also evidence for a more distant structure (C) well behind the A branch. This paper provides the first explanation for the bifurcation. It is caused by ...

We demonstrate that there is a clear statistical correlation between the (X,Y,Z,V_r) phase-space distribution of the outer halo Galactic globular clusters (having 10 kpc <= R_GC <= 40 kpc) and the orbital path of the Sagittarius dwarf spheroidal galaxy (Sgr dSph), as derived by Ibata & Lewis. At least 4 of the sample of 35 globular clusters in this distance range were formerly members of the Sgr galaxy (at the 95 % confidence level), and are now distributed along the Sgr Stre...