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Scientific rationale
Given the standard cosmological model there is far more dark matter than baryonic matter in the Universe. Just where this dark matter resides has been open to speculation and observation since Zwicky first showed that the Coma cluster contains more mass than can be accounted for by the luminosity of its galaxies. Later astronomers have tried to quantify the difference between the mass distribution of the Universe as measured by the location of galaxies compared to that of the underlying mass. The current consensus is that the light from galaxies traces the underlying mass reasonably well, but we have little information on the form of the dark mass that must be associated with the known galaxies. If we are to accept the currently favoured Cold Dark Matter models then we must assume, there are many small dark matter halos within and around larger luminous structures. Given that relatively few are optically detected, one is drawn to the conclusion that the majority of self-gravitating mass concentrations in the Universe remain dark. In this IAU symposium we propose to address the theoretical aspects of dark galaxy formation/evolution and the observational constraints that can be placed on the existence of such elusive objects. A dark galaxy may have reached its current invisible state through one of three pathways. First, it may never have had baryons or it may have lost them all. Second, it may contain baryons, but these have not turned into stars. Third, stars may have formed, but they are now very difficult to detect because their total numbers are very low and/or they are spread out over a large area. In each case the galaxy did not receive or it has lost a fraction of its baryon quota. Each of the above types of dark galaxy offer a different observational and theoretical challenge as to its nature and its role in the grand scheme. The objective of the symposium is to bring together many disjoint observations and models' preditions to reach some consensus on the existence and abundance of dark galaxies. Major Topics: 1) Predictions from CDM or other galaxy formation models about the existence of dark galaxies and their properties. 2) Theoretical predictions from the modelling of the star formation process about the conditions for a galaxy to remain dark. 3) The interpretation of quasar absorption features with regard to the optically dark structures that give rise to many of the absorption lines. 4) Weak lensing both observations and modelling and the interpretation that there are some mass concentrations that have no optical counterparts. 5) X-ray observations of groups and clusters that give rise to mass distributions that are different to that delineated by the optical light. 6) Disturbed galaxies with no apparent perturber; interpreting the data and comparison with numerical simulation. 7) The SZ effect and the detection of optically dark structures. 8) Results from 'blind' 21cm surveys that potentially can find gas rich, but otherwise dark galaxies. 9) The numbers and properties of dark matter dominated dwarf galaxies in the local Universe. 
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