dwarf irregular galaxy
A dwarf galaxy that lacks any apparent structure
or uniformity of shape. Dwarf irregulars (dI) are becoming increasingly
important in understanding the evolution of galaxies in general, because,
with many examples nearby, they enable detailed study of important issues
such as the occurrence of galactic winds, the chemical enrichment of the
interstellar and intergalactic media, and the photometric evolution of galaxies.
In addition, their low level of evolution, as implied by their low metallicity
and high gas content, makes these systems the most similar to primeval galaxies
and, therefore, the most useful to infer the primordial galaxy conditions.
It has also been suggested that dwarf irregulars represent the local counterpart
of faint blue galaxies found in excess in deep galaxy counts.
| Sagittarius Dwarf Irregular Galaxy.