The Morphology of Massive, Gas-Rich Low Surface Brightness Galaxies
One of the more surprising discoveries in the recent work on low surface brightness galaxies (LSBs) is that a significant number are massive and possess significant quantities of atomic gas. Disk galaxies with sizes approaching that of Malin 1 (MHI ∼ 2×1011 M⊙; D ∼ 147 kpc, H0 = 75 km s-1 Mpc-1; Impey and Bothun 1989) have been identified through the use of the Palomar Sky Surveys, with follow-up studies in HI. While many of these galaxies have large amounts of atomic gas and unusually blue disk colors, they have only weak regions of Hα emission, indicating little ongoing massive star formation, and their low surface brightnesses suggest extremely low stellar surface densities. The blue disk colors have ruled out the hypothesis that all LSBs are faded galaxies, but the difficulty in disentangling the difference between low metallicity and young stellar populations based on broadband optical colors has hindered understanding their stellar evolutionary history. It has been suggested (McGaugh 1992) that some LSBs may, in fact, be undergoing their first episodes of star formation since there is little evidence of a difference in the distribution of light in U BV RI images. The LSBs in his sample are largely dwarf systems, however, and the situation is not necessarily comparable for more massive LSBs.
KeywordsStar Formation Surface Brightness Disk Galaxy Massive Star Formation Young Stellar Population
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