Some QSO absorption-line systems (QSOALSs) may arise when a QSO sight line intersects a Magellanic-type irregular galaxy (i.e., a gas-rich dwarf). Much of the complexity in the line profiles of metals can be naturally explained in this manner. The frequency of occurrence of QSOALSs then requires that much of the mass of modern galaxies once resided in a halo of gas-rich dwarfs (at the epoch of QSOALS formation).
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York et al. (1986) studied this question.