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

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. and Thomas, D. (2018) Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey. Monthly Notices of the Royal Astronomical Society, 478 (2), 2006-2018. (doi:10.1093/mnras/sty1039).

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 (≃9.8Gyr) 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 M_V ~ -7.3), its half-light radius (r_h ~ 6.87 pc) and luminosity (M_V ~ -1.7) are more indicative of faint star cluster. Based on the angular size, DES 3, with a value of r_h ~ 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 (r_h ≃ 11.24 pc) and luminosity (M_V ≃ -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.

This record has no associated files available for download.

Contributors

Author: M. Smith

Download statistics