Dark Matter and the Chemical Evolution of Irregular Galaxies

Abstract

We present three types of chemical evolution models for irregular galaxies: closed-box with continuous star formation rates (SFRs), closed-box with bursting SFRs, and O-rich outflow with continuous SFRs. We discuss the chemical evolution of the irregular galaxies NGC 1560 and II Zw 33, and a ``typical'' irregular galaxy. The fraction of low-mass stars needed by our models is larger than that derived for the solar vicinity, but similar to that found in globular clusters. For our typical irregular galaxy we need a mass fraction of about 40% in the form of substellar objects plus non baryonic dark matter inside the Holmberg radius, in good agreement with the results derived for NGC 1560 and II Zw 33 where we do have an independent estimate of the mass fraction in non baryonic dark matter. Closed-box models are better than O-rich outflow models in explaining the C/O and Z/O observed values for our typical irregular galaxy.

arXiv comment14 pages, 2 figure, uses emulateapj.sty package. ApJ in press. New models were added. The order of Tables has been corrected

References in corpus (10)

• Dwarf Galaxies of the Local Group
• The Metallicity Dependence of the CO-to-H${}_2$ Conversion Factor from Observations of Local Group Galaxies
• The Primordial Abundance of He4: An Update
• Chemical Evolution of the Magellanic Clouds: analytical models
• The Evolution of C/O in Dwarf Galaxies from HST Fos Observations
• DY/DZ from fine structure in the Main Sequence based on Hipparcos parallaxes
• A Comparison of Deep HST Luminosity Functions of Four Globular Clusters
• High Carbon in I Zwicky 18: New Results from Hubble Space Telescope Spectroscopy
• Chemical Evolution of Irregular and Blue Compact Galaxies
• The Distance to IC 10 from Near-Infrared Observations of Cepheids

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