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Title: GHOSTS I: A new faint very isolated dwarf galaxy at D = 12 ± 2 Mpc

We report the discovery of a new faint dwarf galaxy, GHOSTS I, using HST/ACS data from one of our GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disk, and Star clusters) fields. Its detected individual stars populate an approximately 1 mag range of its luminosity function (LF). Using synthetic color-magnitude diagrams (CMDs) to compare with the galaxy's CMD, we find that the colors and magnitudes of GHOSTS I's individual stars are most consistent with being young helium-burning and asymptotic giant branch stars at a distance of ∼12 ± 2 Mpc. Morphologically, GHOSTS I appears to be actively forming stars, so we tentatively classify it as a dwarf irregular (dIrr) galaxy, although future Hubble Space Telescope (HST) observations deep enough to resolve a larger magnitude range in its LF are required to make a more secure classification. GHOSTS I's absolute magnitude is M{sub V}∼−9.85{sub −0.33}{sup +0.40}, making it one of the least luminous dIrr galaxies known, and its metallicity is lower than [Fe/H] = –1.5 dex. The half-light radius of GHOSTS I is 226 ± 38 pc and its ellipticity is 0.47 ± 0.07, similar to Milky Way and M31 dwarf satellites at comparable luminosity. There are no luminous massive galaxies ormore » galaxy clusters within ∼4 Mpc from GHOSTS I that could be considered as its host, making it a very isolated dwarf galaxy in the local universe.« less
Authors:
;  [1] ; ;  [2] ; ; ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States)
  2. Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)
  3. Leibniz-Institut für Astrophysik Potsdam, D-14482 Potsdam (Germany)
  4. Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States)
  5. European Space Agency Research Fellow (ESTEC), Keplerlaan 1, 2200-AG Noordwijk (Netherlands)
  6. National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States)
  7. Department of Physics and Astronomy, E7A 317, Macquarie University, Sydney, NSW 2109 (Australia)
Publication Date:
OSTI Identifier:
22348209
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; ASYMPTOTIC SOLUTIONS; CLASSIFICATION; COLOR; COMPARATIVE EVALUATIONS; GALAXY CLUSTERS; HELIUM BURNING; LUMINOSITY; METALLICITY; MILKY WAY; SATELLITES; SPACE; STAR CLUSTERS; STARS; TELESCOPES; UNIVERSE; VISIBLE RADIATION