Star Formation Rates in Low Surface Brightness Galaxies

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Session 12 -- Starburst Galaxies
Display presentation, Monday, 30, 1994, 9:20-6:30

[12.08] Star Formation Rates in Low Surface Brightness Galaxies

T.E. Pickering, C.D. Impey (University of Arizona), J. van Gorkom (Columbia University), G.D. Bothun (University of Oregon)

The low surface brightness (LSB) disk galaxies found in recent surveys (e.g.,\ Schombert et al.\ 1992, AJ, 103, 1107) tend to be blue and gas rich. These properties along with their low mean surface luminosity and {\sc H i} densities imply an inefficient mode of star formation. The H$\alpha$ images that we present of a sample of these galaxies show the weak star formation in these galaxies relative to high surface brightness, Hubble sequence spirals. Most LSB disks harbor only a handful of widely scattered {\sc H ii} regions and generally have low total H$\alpha$ fluxes. However, in some cases these scattered areas of star formation can be quite vigorous. For example, the giant LSB disk galaxy F568-6 contains a complex that is comparable in size, mass, and star formation rate to a luminous irregular galaxy, but contributes only about 5\% of the galaxy's total blue luminosity (Bothun et al.\ 1990, ApJ, 360, 427). We present neutral hydrogen images of some of the largest known LSB galaxies. The gas in these galaxies is distributed in regularly rotating, giant, and also very low {\sc H i} surface brightness disks. A preliminary analysis shows that if most of the gas is in atomic hydrogen, large parts of the disks have total surface densities below the threshold for star formation to set in.

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