The origin of dwarf galaxies, cold dark matter, and biased galaxy formation

The formation of dwarf, diffuse, metal-poor galaxies as a result of supernova-driven winds is reexamined in view of the accumulating data on the systematic properties of dwarfs in the Local Group and in the Virgo Cluster. The observed luminosity-radius-metallicity relations are found to be produced naturally inside dominant halos, with a mass-radius relation that resembles the predictions of the "cold" dark matter cosmological scenario. The critical condition for global gas loss as a result of the first burst of star formation is that the virial velocity be below a critical value on the order of 100 km s<SUP>-1</SUP>. In any hierarchial scenario for galaxy formation, this condition leads to two distinct classes of galaxies as observed: (1) the diffuse dwarfs which mostly originate from typical density perturbations; and (2) the normal, brighter galaxies which can originate only from the highest density peaks. This provides a statistical biasing mechanism for the preferential formation of bright galaxies in denser regions (clusters and superclusters).

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