Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-03-23
Astronomy and Astrophysics
Astrophysics
submitted to ApJL, 3 figures
Scientific paper
We compare the predictions of the Pe\~narrubia et al. (2005) model for the Monoceros stellar ring around the Milky Way with new observational constraints that provide deeper insights on its origin. Recently, Grillmair (2006) found a coherent sub-structure in a panoramic analysis of SDSS data, spanning 5x65 deg^2 above the Galactic plane towards the anticenter. We show here that this structure strikingly matches the prior model predictions in projected position on the sky and the distance (~10 kpc) to within 20%. Newly measured velocities within this sub-structure also match the model predictions perfectly. This match suggests that the model assumptions are correct, namely, that the Monoceros Ring corresponds to a tidal stream wrapping the Milky Way that results from a single disruption event of a satellite (M~5x10e8 M_sun) with a prograde, low-inclination, low-eccentric orbit. Further support for the external origin of the Mon Ring comes from new metalicity measurements of the Mon Ring, which show that this system is much more metal poor than star clusters in the outer Galactic disk at the same radius, and independent detections of RRLyr over-densities in the area that are in excellent agreement with the model predictions. That these observational data can be comprehensively explained by alternative disk heating scenarios seems not likely, but would need to be checked by detailed modeling.
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