Spectroscopic signatures of extratidal stars around the globular clusters NGC 6656 (M 22), NGC 3201, and NGC 1851 from RAVE

¹ Leibniz-Institut für Astrophysics (AIP), An der Sternwarte 16, 14482 Potsdam Germany
e-mail: akunder@aip.de
² Dipartimento di Fisica, Universita di Roma Tor Vergata, Rome, Italy
³ INAF–Osservatorio Astronomico di Roma, via Frascati, 33 00040 Monte Porzio Catone, Italy
⁴ Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, OX1 3NP, UK
⁵ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁶ Department of Physics & Astronomy, Macquarie University, Sydney, NSW 2109, Australia
⁷ Research Centre for Astronomy, Astrophysics and Astrophotonics, Macquarie University, Sydney, NSW 2109, Australia
⁸ Research School of Astronomy & Astrophysics, The Australian National University, Canberra, Australia
⁹ Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK
¹⁰ University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000 Ljubljana, Slovenia
¹¹ Institute for Computational Astrophysics, Dept of Astronomy & Physics, Saint Mary University, Halifax, NS, BH3 3C3, Canada
¹² Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE, UK
¹³ Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006, Australia
¹⁴ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
¹⁵ Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
¹⁶ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
¹⁷ Senior CIfAR Fellow, Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada
¹⁸ Department of Physics and Astronomy, Padova University, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹⁹ Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
²⁰ INAF National Institute of Astrophysics, Astronomical Observatory of Padova, 36012 Asiago ( VI), Italy
²¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Received: 2 May 2014
Accepted: 25 August 2014

Abstract

Context. Stellar population studies of globular clusters have suggested that the brightest clusters in the Galaxy might actually be the remnant nuclei of dwarf spheroidal galaxies. If the present Galactic globular clusters formed within larger stellar systems, they are likely to be surrounded by extratidal halos and/or tails made up of stars that were tidally stripped from their parent systems.

Aims. The stellar surroundings around globular clusters are therefore one of the best places to look for the remnants of an ancient dwarf galaxy. Here an attempt is made to search for tidal debris around the supernovae enriched globular clusters M 22 and NGC 1851, as well as the kinematically unique cluster NGC 3201.

Methods. The stellar parameters from the RAdial Velocity Experiment (RAVE) are used to identify stars with the RAVE metallicities, radial velocities, and elemental abundances that are consistent with the abundance patterns and properties of the stars in M 22, NGC 1851, and NGC 3201.

Results. Discovery of RAVE stars that may be associated with M 22 and NGC 1851 are reported, some of which are at projected distances ~10 degrees away from the core of these clusters. Numerous RAVE stars associated with NGC 3201 suggest that either the tidal radius of this cluster is underestimated or that there are some unbound stars extending a few arc minutes from the edge of the cluster’s radius. No other extratidal stars associated with NGC 3201 could be identified. The bright magnitudes of the RAVE stars make them easy targets for high-resolution follow-up observations, eventually allowing further chemical tagging to solidify (or exclude) stars outside the tidal radius of the cluster as tidal debris. In both our radial velocity histograms of the regions surrounding NGC 1851 and NGC 3201, a peak of stars at ~230 km s^-1 is seen, consistent with extended tidal debris from ω Centauri.