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Abstract

Presented in this paper are results from neutral hydrogen (HI) imaging and analysis of the "Almost Dark" galaxies AGC 219533, AGC 227982, and AGC 268363 using new, higher resolution observations from the Very Large Array (VLA). Selected from the ALFALFA survey, "Almost Dark" galaxies possess significant HI reservoirs but, when the HI data is compared to survey-depth ground-based optical imaging, their optical stellar counterparts have extremely low surface brightnesses. AGC 219533 is one such object. The other two sources, AGC 227982 and AGC 26833, were candidate dark galaxies, as no stellar counterpart was identified in initial ALFALFA optical matching, and as such they possessed some of the most extreme levels of suppressed star formation amongst the isolated sources in the ALFALFA catalog. The new multiconfiguration, high angular (~20") and spectral (1.7 km/s) resolution HI observations presented here have produced spatially resolved column density and velocity distribution moment maps where the HI has been localized. HI masses are derived from VLA flux integral values and ALFALFA distance estimates, and are consistent with those derived from ALFALFA fluxes. Comparison of our resolved HI observations to Sloan Digitized Sky Survey (SDSS) optical images reveals previously unknown optical components for AGC 227982 and AGC 268363, and confirms the association with a very low surface brightness stellar counterpart for AGC 219533. These new results eliminate the three galaxies' candidacy as dark galaxies.

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