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Title: THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?

We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density ofmore » the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.« less
Authors:
; ; ; ; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11]
  1. Instituto de Astrofísica de Canarias, La Laguna, Tenerife (Spain)
  2. Institut für Theoretische Physik, University of Zurich, Zürich (Switzerland)
  3. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
  4. INAF-Osservatorio Astronomico di Collurania, Teramo (Italy)
  5. School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, TAS 7005 (Australia)
  6. Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States)
  7. Department of Physics and Astronomy, University of Victoria, PO Box 1700, STN CSC, Victoria, BC V8W 3P6 (Canada)
  8. Kapteyn Astronomical Institute, Landleven 12, NL-9747 AD Groningen (Netherlands)
  9. Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN (United States)
  10. Herzberg Astronomy and Astrophysics, National Research Council Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
  11. Astronomy Department, University of Washington, Box 351580, Seattle, WA (United States)
Publication Date:
OSTI Identifier:
22518880
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 811; 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; COLOR; DENSITY; DIAGRAMS; DWARF STARS; ENVIRONMENTAL EFFECTS; GALACTIC EVOLUTION; MILKY WAY; MORPHOLOGY; STAR EVOLUTION; STARS