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A. K. Leroy (UC Berkeley)
Nearby dwarf galaxies represent the best laboratories to study molecular gas and star formation under "primitive" conditions in detail. I will show the relationship between galaxy properties and molecular gas content and between molecular gas content and star formation in nearby dwarfs. These include a survey for CO J=1->0 emission from 120 nearby dwarfs with IRAS detections and case studies of the Local Group dwarf irregulars IC 10 and the Small Magellanic Cloud. In the survey, we detect CO in 28 dwarfs; the median mass of a detected dwarf is comparable to that of the LMC. These galaxies obey the same radio-continuum to CO relation as large spiral galaxies, which we interpret as evidence for a common star formation law. The molecular content normalized by the stellar mass of the galaxy shows minimal correlation with other galaxy properties. Therefore, we argue that the stellar potential well plays a crucial role in the transformation of atomic to molecular gas.
The two Local Group dwarfs, IC 10 and the SMC, have masses an order of magnitude lower than those of the typical dwarfs in the survey. In IC 10 the importance of the stellar potential well is borne out by the correspondence between the hydrostatic pressure and the fraction of gas in the molecular phase. In both IC 10 and the SMC, however, the rate of star formation per unit molecular gas is much higher than in either the survey sample or large spirals. This may reflect changes to the CO-to-H2 conversion factor or be indicative of real changes in the efficiency of star formation in these systems. Both conclusions are at odds with the surprising similarity between the properties of GMCs in dwarf galaxies and spiral galaxies in the Local Group.
This work has been supported by NSF grant 0228963 to the Radio Astronomy Laboratory at UC Berkeley.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.