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Advances in Astronomy
Volume 2010 (2010), Article ID 278434, 21 pages
http://dx.doi.org/10.1155/2010/278434
Review Article

Environmental Mechanisms Shaping the Nature of Dwarf Spheroidal Galaxies: The View of Computer Simulations

Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland

Received 14 June 2009; Revised 17 September 2009; Accepted 1 October 2009

Academic Editor: Andrey V. Kravtsov

Copyright © 2010 Lucio Mayer. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We review numerical works carried out over the last decade on the role of environmental mechanisms in shaping nature of the faintest galaxies known, dwarf spheroidals (dSphs). The combination of tidally induced morphological transformation, termed tidal stirring, with mass loss due to tidal and ram-pressure stripping aided by heating due to the cosmic ionizing background can turn late-type dwarfs resembling present-day dIrrs into classic dSphs. The time of infall into the primary halo is shown to be a key parameter. Dwarfs accreting at 𝑧 > 1 , when the cosmic ultraviolet ionizing flux was much higher than today, and was thus able to keep the gas in the dwarfs warm and diffuse, were rapidly stripped of their baryons via ram pressure and tidal forces, producing very dark-matter-dominated objects with truncated star-formation histories, such as the Draco dSph. The low star-formation efficiency expected in such low-metallicity objects prior to their infall was crucial for keeping their disks gas dominated until stripping took over. Therefore gas stripping along with inefficient star-formation provides a new feedback mechanism, alternative to photoevaporation or supernovae feedback, playing a crucial role in dwarf galaxy formation and evolution. We also discuss how the ultra-faint dSphs belong to a different population of lower-mass dwarf satellites that were mostly shaped by reionization rather than by environmental mechanisms (“reionization fossils”). Finally, we scrutinize the various caveats in the current understanding of environmental effects as well as other recent ideas on the origin of Local Group dSphs.