Star formation histories of irregular galaxies

• Published in: The Astrophysical journal Vol. 284; no. 2; pp. 544 - 556
• Main Authors: GALLAGHER, J. S. III, HUNTER, D. A, TUTUKOV, A. V
• Format: Journal Article
• Language: English
• Published: Chicago, IL University of Chicago Press 15.09.1984
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Interstellar medium (ism) and nebulae in external galaxies; Stellar systems. Galactic and extragalactic objects and systems. The universe; Evolution; Stellar formation; Spiral galaxies; Mass function; Irregular galaxies
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/162437

The star formation histories of a selection of irregular and spiral galaxies are analyzed using three parameters for sampling the star formation rate in different epochs: galaxy mass; blue luminosity; and Lyman continuum photon fluxes derived from Hz luminosities. It is found that for most irregular galaxies these parameters are consistent with a nearly constant SFR and a Salpeter initial mass function over the lifetimes of the galaxies. The spiral and high-mass irregular galaxies appear to have had a constant SFR over the past few billion years but also have high total mass indicating either an early phase of intense star formation or the presence of dark matter. Global bursts of star formation among irregular galaxies appear to be rare. The constant SFR history implies that the simple classical model in which star formation is proportional to gas density in a closed system cannot be correct for irregular galaxies. Some alternative models for constant global SFRs are discussed.