Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey. Issue 2 (25th April 2018)

• Record Type: Journal Article
• Authors: 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-Lévy, A; Bertin, E; Brooks, D; Carnero Rosell, A; Carrasco Kind, M; Carretero, J; Crocce, M; Davis, C; Doel, P; Eifler, T F; Flaugher, B; García-Bellido, J; Gerdes, D W; Gruen, D; Gruendl, R A; Gutierrez, G; Honscheid, K; James, D J; Kuehn, K; Kuropatkin, N; Miquel, R; Nichol, R C; Plazas, A A; Sanchez, E; Scarpine, V; Schindler, R; Sevilla-Noarbe, I; Smith, M; Soares-Santos, M; Sobreira, F; Suchyta, E; Tarle, G; Thomas, D;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 478:Issue 2(2018)
• Page Start: 2006
• Page End: 2018
• Publication Date: 2018-04-25
• Subjects: globular clusters: general -- Galaxy: halo; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty1039
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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 MV ∼ −7.3), its half-light radius ( r h ∼ 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 r h ∼ 0${^{\prime}_{.}}$ 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 ( 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.