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The Discovery of an Ultra-faint Star Cluster in the Constellation of Ursa Minor

Muñoz, R. R. and Geha, M. and Côté, P. and Vargas, L. C. and Santana, F. A. and Stetson, P. and Simon, J. D. and Djorgovski, S. G. (2012) The Discovery of an Ultra-faint Star Cluster in the Constellation of Ursa Minor. Astrophysical Journal Letters, 753 (1). Art. No. L15. ISSN 2041-8205. doi:10.1088/2041-8205/753/1/L15.

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We report the discovery of a new ultra-faint globular cluster in the constellation of Ursa Minor, based on stellar photometry from the MegaCam imager at the Canada-France-Hawaii Telescope. We find that this cluster, Muñoz 1, is located at a distance of 45 ± 5 kpc and at a projected distance of only 45' from the center of the Ursa Minor dwarf spheroidal galaxy. Using a maximum-likelihood technique we measure a half-light radius of 0farcm5, or equivalently 7 pc, and an ellipticity consistent with being zero. We estimate its absolute magnitude to be M_V = –0.4 ± 0.9, which corresponds to L_V = 120^(+160)_–(65) L_☉ and we measure a heliocentric radial velocity of –137 ± 4 km s^(–1) based on Keck/DEIMOS spectroscopy. This new satellite is separate from Ursa Minor by ~30 kpc and 110 km s^(–1) suggesting the cluster is not obviously associated with the dSph, despite the very close angular separation. Based on its photometric properties and structural parameters we conclude that Muñoz 1 is a new ultra-faint stellar cluster. Along with Segue 3 this is one of the faintest stellar clusters known to date.

Item Type:Article
Related URLs:
URLURL TypeDescription
Geha, M.0000-0002-7007-9725
Côté, P.0000-0003-1184-8114
Vargas, L. C.0000-0001-7155-0040
Santana, F. A.0000-0002-4023-7649
Stetson, P.0000-0001-6074-6830
Djorgovski, S. G.0000-0002-0603-3087
Additional Information:© 2012 The American Astronomical Society. Received 2012 March 12; accepted 2012 April 24; published 2012 June 15. We thank the referee for useful comments that helped improve this paper. We acknowledge Robert Zinn for useful discussions. This work was supported in part by the facilities and staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center. R.R.M. acknowledges support from the GEMINI-CONICYT Fund, allocated to the project N◦32080010, from CONICYT through project BASAL PFB-06 and the Fondo Nacional de Desarrollo Científico y Tecnolόgico (Fondecyt project N◦1120013). M. G. acknowledges support from National Science Foundation under award number AST-0908752 and the Alfred P. Sloan Foundation. S.G.D. acknowledges partial support from NSF grant AST-0909182. Based on observations obtained at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Spectroscopic data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.
Funding AgencyGrant Number
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)32080010
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1120013
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords: Galaxy: halo; globular clusters: general; Local Group
Issue or Number:1
Record Number:CaltechAUTHORS:20120723-110203782
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Official Citation:The Discovery of an Ultra-faint Star Cluster in the Constellation of Ursa Minor R. R. Muñoz et al. 2012 ApJ 753 L15
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32641
Deposited By: Ruth Sustaita
Deposited On:24 Jul 2012 15:40
Last Modified:09 Nov 2021 21:28

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