Dwarf Galaxies with Active Star Formation

Abstract

Dwarf galaxies with active star formation play a significant role in the family of starburst galaxies. They share a number of properties with their giant brethren, while their lower mass leads to some charateristics that are specific to star forming dwarfs. To see both similarities and differences, in this brief review, we focus on the different phases of the interstellar medium in dwarfs. The hot gas, typically observed in X‐rays, can, least in some cases, blow out of the galaxies. This phenomenon, still visible today, also provides an important mechanism for the metal enrichment of the intergalactic medium (IGM) in the early universe. The neutral gas, HI, sometimes extends into huge halos surrounding the optical galaxies. HI companions seem to be frequent, possibly pointing to infall and interaction as necessary means of feeding the starburst. On small scales, some dwarf galaxies show numerous HI holes, implying propagating star formation and allowing the investigation of early phases of what later may become a blow‐out of the gas. Molecular gas, the site of actual star formation, is notoriously difficult to detect in dwarfs. The reasons for this are well understood and not related to a dearth of molecular material, but rather the low metallicity environment chracteristic for dwarf galaxies. Sensitive observations have provided a number of maps of molecular gas in dwarfs and the determination of gas properties is slowly becoming possible.