Title: Globular Cluster Streams as Galactic High-Precision Scales

Abstract:
Using the example of the tidal stream of the Milky Way globular cluster Palomar 5 (Pal 5), we 
demonstrate how observational data of tidal streams can be efficiently reduced in dimensionality 
and modeled in a Bayesian framework. Our approach combines detection of stream 
overdensities by a Difference-of-Gaussians process with fast streakline models of globular 
cluster streams and a Markov chain Monte Carlo machinery. By generating ~10^7 model 
streams, we show that the unique geometry of the Pal 5 debris yields powerful constraints on 
the solar position and motion, the Milky Way and Pal 5 itself, which we allowed to vary in the 
models over large ranges without additional prior information. Using only readily-available SDSS 
data and a few radial velocities from the literature, we find that the distance of the Sun from the 
Galactic Center is 8.30+/-0.25 kpc, and the transverse velocity is 253+/-16 km/s. Both 
estimates are in excellent agreement with independent measurements of these two quantities, 
which usually require significantly more expensive data. We determine the Galactic mass within 
Pal 5''s apogalactic radius of 19 kpc to be (2.1+/-0.4)x10^11 M_sun.
Moreover, assuming a standard disk model, we find the potential of the dark halo with a 
flattening of q_z = 0.95^+0.16_-0.12 to be essentially spherical - at least within the radial range 
that is effectively probed by Pal 5. We also determine Pal 5''s mass, distance and proper 
motion independently from other methods, which enables us to perform vital cross-checks. Our 
inferred heliocentric distance of Pal 5 is 23.6^+0.8_-0.7 kpc, in perfect agreement with, and 
more precise than estimates from isochrone fitting of deep HST imaging data. We conclude that 
finding and modeling more globular cluster streams is an efficient way for mapping out the 
structure of our Galaxy to high precision.