Eight New Milky Way Companions Discovered in First-year Dark Energy Survey Data

K. Bechtol , A. Drlica-Wagner , E. Balbinot , A. Pieres , J. D. Simon , B. Yanny , B. Santiago , R. H. Wechsler , J. Frieman , A. R. Walker , P. Williams , E. Rozo , E. S. Rykoff , A. Queiroz , E. Luque , A. Benoit-Lévy , D. Tucker , I. Sevilla , R. A. Gruendl , L. N. da Costa , A. Fausti Neto , M. A. G. Maia , T. Abbott , S. Allam , R. Armstrong , A. H. Bauer , G. M. Bernstein , R. A. Bernstein , E. Bertin (1) , D. Brooks , E. Buckley-Geer , D. L. Burke , A. Carnero Rosell , F. J. Castander , R. Covarrubias , C. B. d'Andrea , D. L. Depoy , S. Desai , H. T. Diehl , T. F. Eifler , J. Estrada , A. E. Evrard , E. Fernandez , D. A. Finley , B. Flaugher , E. Gaztanaga , D. Gerdes , L. Girardi , M. Gladders , D. Gruen , G. Gutierrez , J. Hao , K. Honscheid , B. Jain , D. James , S. Kent , R. Kron , K. Kuehn , N. Kuropatkin , O. Lahav , T. S. Li , H. Lin , M. Makler , M. March , J. Marshall , P. Martini , K. W. Merritt , C. Miller , R. Miquel , J. Mohr , E. Neilsen , R. Nichol , B. Nord , R. Ogando , J. Peoples , D. Petravick , A. A. Plazas , A. K. Romer , A. Roodman , M. Sako , E. Sanchez , V. Scarpine , M. Schubnell , R. C. Smith , M. Soares-Santos , F. Sobreira , E. Suchyta , M. E. C. Swanson , G. Tarle , J. Thaler , D. Thomas , W. Wester , J. Zuntz

1 IAP - Institut d'Astrophysique de Paris

We report the discovery of eight new Milky Way companions in ∼ 1800 {{deg}}² of optical imaging data collected during the first year of the Dark Energy Survey (DES). Each system is identified as a statistically significant over-density of individual stars consistent with the expected isochrone and luminosity function of an old and metal-poor stellar population. The objects span a wide range of absolute magnitudes (M_V from -2.2 to -7.4 {mag}), physical sizes (10-170 {pc}), and heliocentric distances (30-330 {kpc}). Based on the low surface brightnesses, large physical sizes, and/or large Galactocentric distances of these objects, several are likely to be new ultra-faint satellite galaxies of the Milky Way and/or Magellanic Clouds. We introduce a likelihood-based algorithm to search for and characterize stellar over-densities, as well as identify stars with high satellite membership probabilities. We also present completeness estimates for detecting ultra-faint galaxies of varying luminosities, sizes, and heliocentric distances in the first-year DES data.

Keywords: galaxies: dwarf; Local Group; Astrophysics - Astrophysics of Galaxies

Domains: Sciences of the Universe [physics]

K. Bechtol, A. Drlica-Wagner, E. Balbinot, A. Pieres, J. D. Simon, et al.. Eight New Milky Way Companions Discovered in First-year Dark Energy Survey Data. The Astrophysical Journal, 2015, 807, ⟨10.1088/0004-637X/807/1/50⟩. ⟨insu-03644908⟩