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


  • 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. 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 (9.8Gyr) 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 (12.6Gyr) 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 MilkyWay 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.

published proceedings


altmetric score

  • 8.6

author list (cited authors)

  • Luque, E., Santiago, B., Pieres, A., Marshall, J. L., Pace, A. B., Kron, R., ... Thomas, D.

citation count

  • 13

complete list of authors

  • Luque, E||Santiago, B||Pieres, A||Marshall, JL||Pace, AB||Kron, R||Drlica-Wagner, A||Queiroz, A||Balbinot, E||dal Ponte, M||Fausti Neto, A||da Costa, LN||Maia, MAG||Walker, AR||Abdalla, FB||Allam, S||Annis, J||Bechtol, K||Benoit-Lévy, A||Bertin, E||Brooks, D||Carnero Rosell, A||Carrasco Kind, M||Carretero, J||Crocce, M||Davis, C||Doel, P||Eifler, TF||Flaugher, B||García-Bellido, J||Gerdes, DW||Gruen, D||Gruendl, RA||Gutierrez, G||Honscheid, K||James, DJ||Kuehn, K||Kuropatkin, N||Miquel, R||Nichol, RC||Plazas, AA||Sanchez, E||Scarpine, V||Schindler, R||Sevilla-Noarbe, I||Smith, M||Soares-Santos, M||Sobreira, F||Suchyta, E||Tarle, G||Thomas, D

publication date

  • April 2018