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 Wayglobular 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 embeddedin a diffuse stellar envelope extending to a radial distance of at least ~60 arcmin (~210 pc)- five times the nominal tidal radius of the cluster. The envelope appears nearly circular inshape, has a radial density decline well described by a power law of index γ =-2.2 ± 0.2, andcontains approximately 1.6 per cent of the luminosity of the entire system. While the originof 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 ironand 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.