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

作者：Luque E; Santiago B; Pieres A; Marshall J L; Pace A B; Kron R; Drlica Wagner A; Queiroz A; Balbinot E; dal Ponte M; Fausti Neto A; da Costa L N; Maia M A G; Walker A R; Abdalla F B; Allam S; Annis J; Bechtol K; Benoit Levy A; Bertin E; Brooks D; Carnero Rosell A; Kind M Carrasco; Carretero J; Crocce M; Davis C; Doel P; Eifler T F; Flaugher B; Garcia Bellido J; Gerdes D W; Gruen D; Gruendl R A; Gutierrez G

来源：Monthly Notices of the Royal Astronomical Society, 2018, 478(2): 2006-2018.

DOI：10.1093/mnras/sty1039

• globular clusters: general
• Galaxy: halo

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 similar or equal to 76.2 kpc and it is dominated by an old (similar or equal to 9.8Gyr) and metal-poor ([Fe/H] similar or equal to -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 similar to 10(5) M-circle dot and luminosity M-V similar to -7.3), its half-light radius (r(h) similar to 6.87 pc) and luminosity (M-V similar to -1.7) are more indicative of faint star cluster. Based on the angular size, DES 3, with a value of r(h) similar to 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 (similar or equal to 12.6Gyr) and metallicity ([Fe/H] similar or equal to -2.01) estimates for this object. The half-light radius (r(h) similar or equal to 11.24 pc) and luminosity (M-V similar or equal to -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.

• 出版日期2018-8