Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 808, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/808/2/L39
Keywords
galaxies: dwarf; galaxies: individual (Horologium II); galaxies: stellar content; Galaxy: halo; Local Group
Categories
Funding
- Australian Research Council [DP150100862]
- Robert Martin Ayers Sciences Fund
- U.S. Department of Energy
- U.S. National Science Foundation
- Ministry of Science and Education of Spain
- Science and Technology Facilities Council of the United Kingdom
- Higher Education Funding Council for England
- National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign
- Kavli Institute of Cosmological Physics at the University of Chicago
- Center for Cosmology and Astro-Particle Physics at the Ohio State University
- Mitchell Institute for Fundamental Physics and Astronomy at Texas AM University
- Financiadora de Estudos e Projetos
- Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico
- Ministerio da Ciencia, Tecnologia e Inovacao
- Argonne National Laboratory
- University of California at Santa Cruz
- University of Cambridge
- Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid
- University of Chicago
- University College London
- DES-Brazil Consortium
- University of Edinburgh
- Eidgenossische Technische Hochschule (ETH) Zurich
- Fermi National Accelerator Laboratory
- University of Illinois at Urbana-Champaign
- Institut de Ciencies de l'Espai (IEEC/CSIC)
- Institut de Fisica d'Altes Energies
- Lawrence Berkeley National Laboratory
- Ludwig-Maximilians Universitat Munchen
- University of Michigan
- National Optical Astronomy Observatory
- University of Nottingham
- Ohio State University
- University of Pennsylvania
- University of Portsmouth
- SLAC National Accelerator Laboratory
- Stanford University
- University of Sussex
- Texas AM University
- unassociated Excellence Cluster universe
- Deutsche Forschungsgemeinschaft
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We report the discovery of a new ultra-faint Milky Way satellite candidate, Horologium II (Hor II), detected in the Dark Energy Survey Y1A1 public data. Hor II features a half-light radius of r(h) = 47 +/- 10 pc and a total luminosity of M-V = -2.6(-0.3)(+0.2) that place it in the realm of ultra-faint dwarf galaxies on the size-luminosity plane. The stellar population of the new satellite is consistent with an old (similar to 13.5 Gyr) and metal-poor ([Fe/H] similar to -2.1) isochrone at a distance modulus of (m - M) = 19.46 +/- 0.20, or a heliocentric distance of 78 +/- 8 kpc, in the color-magnitude diagram. Hor II has a distance similar to the Sculptor dwarf spheroidal galaxy (similar to 82 kpc) and the recently reported ultra-faint satellites Eridanus III (87 +/- 8 kpc) and Horologium I (79 +/- 8 kpc). All four satellites are well aligned on the sky, which suggests a possible common origin. As Sculptor is moving on a retrograde orbit within the Vast Polar Structure when compared to the other classical MW satellite galaxies including the Magellanic Clouds, this hypothesis can be tested once proper motion measurements become available.
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