The Outer Envelopes of Globular Clusters. I. NGC 7089 (M2)
  We present the results of a wide-field imaging survey of the periphery of the
Milky Way globular cluster NGC 7089 (M2). Data were obtained with MegaCam on
the Magellan Clay Telescope, and the Dark Energy Camera on the Blanco
Telescope. We find that M2 is embedded in a diffuse stellar envelope extending
to a radial distance of at least $\sim 60^{\prime}$ ($\sim 210$ pc) -- five
times the nominal tidal radius of the cluster. The envelope appears nearly
circular in shape, has a radial density decline well described by a power law
of index $\gamma = -2.2 \pm 0.2$, and contains approximately $1.6\%$ of the
luminosity of the entire system. While the origin of the envelope cannot be
robustly identified using the presently available data, the fact that M2 also
hosts stellar populations exhibiting a broad dispersion in the abundances of
both iron and a variety of neutron capture elements suggests that this object
might plausibly constitute the stripped nucleus of a dwarf Galaxy that was long
ago accreted and destroyed by the Milky Way.
