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Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey

Luque, E. and Eifler, T. F. (2018) Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey. Monthly Notices of the Royal Astronomical Society, 478 (2). pp. 2006-2018. ISSN 0035-8711.

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We report the discovery of a new star cluster, DES 3, in the constellation of Indus, and deeper observations of the previously identified satellite DES J0222.7−5217 (Eridanus III). DES 3 was detected as a stellar overdensity in first-year Dark Energy Survey data, and confirmed with deeper photometry from the 4.1-m Southern Astrophysical Research (SOAR) telescope. The new system was detected with a relatively high significance and appears in the DES images as a compact concentration of faint blue point sources. We determine that DES 3 is located at a heliocentric distance of ≃76.2 kpc and it is dominated by an old (≃9.8 Gyr) and metal-poor ([Fe/H] ≃ −1.84) population. While the age and metallicity values of DES 3 are comparable to typical globular clusters (objects with a high stellar density, stellar mass of ∼10^5 M⊙ and luminosity M_V ∼ −7.3), its half-light radius (r_h ∼ 6.87 pc) and luminosity (M_V ∼ −1.7) are more indicative of faint star cluster. Based on the angular size, DES 3, with a value of r_h ∼ 0.”31, is among the smallest faint star clusters known to date. Furthermore, using deeper imaging of DES J0222.7−5217 taken with the SOAR telescope, we update structural parameters and perform the first isochrone modelling. Our analysis yields the first age (≃12.6 Gyr) and metallicity ([Fe/H] ≃ −2.01) estimates for this object. The half-light radius (r_h ≃ 11.24 pc) and luminosity (M_V ≃ −2.4) of DES J0222.7−5217 suggest that it is likely a faint star cluster. The discovery of DES 3 indicates that the census of stellar systems in the Milky Way is still far from complete, and demonstrates the power of modern wide-field imaging surveys to improve our knowledge of the Galaxy’s satellite population.

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Additional Information:© 2018 Crown copyright. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 April 19. Received 2018 April 17; in original form 2017 September 17. Published: 25 April 2018. We thank the anonymous referee for interesting remarks. This paper has gone through internal review by the DES collaboration. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovação, the Deutsche Forschungsgemeinschaft and the Collaborating Institutions in the Dark Energy Survey. The Collaborating Institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, the Eidgenössische Technische Hochschule (ETH) Zürich, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Institut de Ciències de l’Espai (IEEC/CSIC), the Institut de Física d’Altes Energies, Lawrence Berkeley National Laboratory, the Ludwig-Maximilians Universität München and the associated Excellence Cluster Universe, the University of Michigan, the National Optical Astronomy Observatory, the University of Nottingham, The Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, Texas A&M University, and the OzDES Membership Consortium. Based in part on observations at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. The DES data management system is supported by the National Science Foundation under Grant Numbers AST-1138766 and AST-1536171. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2015-71825, ESP2015-88861, FPA2015-68048, SEV-2012-0234, SEV-2016-0597, and MDM-2015-0509, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA programme of the Generalitat de Catalunya. Research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. We acknowledge support from the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Based on observations obtained at the SOAR telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). EB acknowledges financial support from the European Research Council (StG-335936).
Funding AgencyGrant Number
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2015-71825
Ministerio de Economía, Industria y Competitividad (MINECO)ESP2015-88861
Ministerio de Economía, Industria y Competitividad (MINECO)FPA2015-68048
Centro de Excelencia Severo OchoaSEV-2012-0234
Centro de Excelencia Severo OchoaSEV-2016-0597
Ministerio de Economía, Industria y Competitividad (MINECO)MDM-2015-0509
European Regional Development Fund, EstoniaUNSPECIFIED
Generalitat de CatalunyaUNSPECIFIED
European Research Council (ERC)240672
European Research Council (ERC)291329
European Research Council (ERC)306478
Australian Research CouncilCE110001020
Department of Energy (DOE)DE-AC02-07CH11359
European Research Council (ERC)335936
Subject Keywords:globular clusters: general –Galaxy: halo
Record Number:CaltechAUTHORS:20180809-130008201
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Official Citation:E Luque, B Santiago, A Pieres, J L Marshall, A B Pace, R Kron, A Drlica-Wagner, A Queiroz, E Balbinot, M dal Ponte, A Fausti Neto, L N da Costa, M A G Maia, A R Walker, F B Abdalla, S Allam, J Annis, K Bechtol, A Benoit-Lévy, E Bertin, D Brooks, A Carnero Rosell, M Carrasco Kind, J Carretero, M Crocce, C Davis, P Doel, T F Eifler, B Flaugher, J García-Bellido, D W Gerdes, D Gruen, R A Gruendl, G Gutierrez, K Honscheid, D J James, K Kuehn, N Kuropatkin, R Miquel, R C Nichol, A A Plazas, E Sanchez, V Scarpine, R Schindler, I Sevilla-Noarbe, M Smith, M Soares-Santos, F Sobreira, E Suchyta, G Tarle, D Thomas; Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey, Monthly Notices of the Royal Astronomical Society, Volume 478, Issue 2, 1 August 2018, Pages 2006–2018,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88698
Deposited By: Tony Diaz
Deposited On:09 Aug 2018 20:11
Last Modified:09 Aug 2018 20:11

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