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

Journal Article · · Monthly Notices of the Royal Astronomical Society
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  1. Instituto de Física, UFRGS, Porto Alegre (Brazil); Laboratório Interinstitucional de e-Astronomia - LIneA, Rio de Janeiro (Brazil)
  2. Texas A & M Univ., College Station, TX (United States). George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Univ. of Chicago, IL (United States). Kavli Institute for Cosmological Physics
  4. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  5. University of Surrey, Guildford (United Kingdom). Department of Physics
  6. Laboratório Interinstitucional de e-Astronomia - LIneA, Rio de Janeiro (Brazil)
  7. Laboratório Interinstitucional de e-Astronomia - LIneA, Rio de Janeiro (Brazil); Observatório Nacional, Rio de Janeiro (Brazil)
  8. Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, La Serena (Chile)
  9. University College London (United Kingdom). Department of Physics and Astronomy; Rhodes University, Grahamstown (South Africa). Department of Physics and Electronics
  10. LSST, Tucson, AZ (United States)
  11. University College London (United Kingdom). Department of Physics and Astronomy; CNRS, Institut d’Astrophysique de Paris (France). Sorbonne Universités, UPMC Univ Paris
  12. CNRS, Institut d’Astrophysique de Paris (France). Sorbonne Universités, UPMC Univ Paris
  13. University College London (United Kingdom). Department of Physics and Astronomy
  14. Univ. of Illinois, Urbana, IL (United States). Department of Astronomy; National Center for Supercomputing Applications, Urbana, IL (United States)
  15. The Barcelona Institute of Science and Technology, Campus UAB (Spain). Institut de Física d’Altes Energies (IFAE)
  16. Institute of Space Sciences, IEEC-CSIC, Campus UAB, Barcelona (Spain)
  17. Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics and Cosmology
  18. California Inst. of Technology (CalTech), Pasadena, CA (United States). Department of Physics and Jet Propulsion Lab.
  19. Universidad Autonoma de Madrid (Spain). Instituto de Fisica Teorica UAM/CSIC
  20. Univ. of Michigan, Ann Arbor, MI (United States). Department of Astronomy and Department of Physics
  21. Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics and Cosmology; SLAC National Accelerator Lab., Menlo Park, CA (United States)
  22. The Ohio State Univ., Columbus, OH (United States). Center for Cosmology and Astro-Particle Physics and Department of Physics
  23. Univ. of Washington, Seattle, WA (United States). Astronomy Department
  24. Australian Astronomical Observatory, North Ryde, NSW (Australia)
  25. University of Portsmouth (United Kingdom). Institute of Cosmology and Gravitation
  26. California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  27. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid (Spain)
  28. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  29. University of Southampton (United Kingdom). School of Physics and Astronomy
  30. Laboratório Interinstitucional de e-Astronomia - LIneA, Rio de Janeiro (Brazil); Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, Campinas (Brazil)
  31. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Computer Science and Mathematics Division
  32. Univ. of Michigan, Ann Arbor, MI (United States). Department of Physics
  33. University of Portsmouth (United Kingdom). Institute of Cosmology and Gravitation,
+ Show Author Affiliations

In this paper, 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. Finally, 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.

Research Organization:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE; USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR)
Grant/Contract Number:
AC02-76SF00515; AST-1138766; AST-1536171; AYA2015-71825; ESP2015-88861; FPA2015-68048; SEV-2012-0234; SEV-2016-0597; MDM-2015-0509; 240672; 291329; 306478; AC05-00OR22725
OSTI ID:
1468950
Alternate ID(s):
OSTI ID: 1468043
Journal Information:
Monthly Notices of the Royal Astronomical Society, Vol. 478, Issue 2; ISSN 0035-8711
Publisher:
Royal Astronomical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 13 works
Citation information provided by
Web of Science

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Cited By (7)

Nine tiny star clusters in Gaia DR1, PS1, and DES journal January 2019
Robust velocity dispersion and binary population modelling of the ultrafaint dwarf galaxy Reticulum II journal June 2019
The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2 journal June 2019
Stellar Streams Discovered in the Dark Energy Survey journal July 2018
Proper Motions of Milky Way Ultra-faint Satellites with Gaia DR2 × DES DR1 journal April 2019
A Faint Halo Star Cluster Discovered in the Blanco Imaging of the Southern Sky Survey journal April 2019
The hidden giant: Discovery of an enormous Galactic dwarf satellite in Gaia DR2 text January 2019

Figures / Tables (12)

Figure 1(p. 3)figure Figure 1
Figure 2(p. 4)figure Figure 2
Figure 3(p. 4)figure Figure 3
Figure 4(p. 5)figure Figure 4
Table 1(p. 5)table Table 1
Figure 5(p. 6)figure Figure 5
Table 2(p. 6)table Table 2
Figure 6(p. 7)figure Figure 6
Figure 7(p. 7)figure Figure 7
Figure 8(p. 8)figure Figure 8
Table 3(p. 8)table Table 3
Figure 9(p. 9)figure Figure 9

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