THE ACS LCID PROJECT: On the ORIGIN of DWARF GALAXY TYPES - A MANIFESTATION of the HALO ASSEMBLY BIAS?

Carme Gallart, Matteo Monelli, Lucio Mayer, Antonio Aparicio, Giuseppina Battaglia, Edouard J. Bernard, Santi Cassisi, Andrew A. Cole, Andrew E. Dolphin, Igor Drozdovsky, Sebastian L. Hidalgo, Julio F. Navarro, Stefania Salvadori, Evan D. Skillman, Peter B. Stetson, Daniel R. Weisz

    Research output: Contribution to journalArticlepeer-review

    46 Scopus citations

    Abstract

    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.

    Original languageEnglish (US)
    Article numberL18
    JournalAstrophysical Journal Letters
    Volume811
    Issue number2
    DOIs
    StatePublished - Oct 1 2015

    Bibliographical note

    Publisher Copyright:
    © 2015. The American Astronomical Society. All rights reserved.

    Keywords

    • galaxies: dwarf
    • galaxies: evolution
    • galaxies: formation

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