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

Research output: Contribution to journalArticle

  • 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
  • A. A. Plazas
  • E. Sanchez
  • V. Scarpine
  • R. Schindler
  • I. Sevilla-Noarbe
  • M. Smith
  • M. Soares-Santos
  • F. Sobreira
  • E. Suchyta
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 ∼105 M⊙ and luminosity MV ∼ −7.3), its half-light radius (rh ∼ 6.87 pc) and luminosity (MV ∼ −1.7) are more indicative of faint star cluster. Based on the angular size, DES 3, with a value of rh ∼ 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 (rh ≃ 11.24 pc) and luminosity (MV ≃ −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.
Original languageEnglish
Pages (from-to)2006-2018
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date25 Apr 2018
Publication statusPublished - 1 Aug 2018


  • Deep SOAR follow-up photometry

    Rights statement: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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