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L van Zee (Indiana University)
HI synthesis observations of UGC 5288 reveal that the majority of its HI is located beyond the stellar component in a well ordered, slightly warped, disk. The HI flux density spatially coincident with the stellar component corresponds to less than 1/8 of the total gas content of this compact dwarf irregular galaxy. However, despite the presence of significant gas mass at large radii, the gas density of the outer gas disk is more than a factor of 10 below the Toomre instability threshold. Similar to NGC 2915, the optical morphology of UGC 5288 is highly suggestive of a bar-like object embedded in an extended, low density, gaseous disk. Possible origins of the diffuse gas disk around UGC 5288 include (1) the disk is the remnant of a galactic fountain (perhaps created after a past star burst episode); (2) the disk is tidal debris created during a recent encounter; and (3) the disk is a remnant of the nascent material from which the galaxy collapsed. We discuss observational constraints on the origin and evolution of the gas disk; in particular, given its local environment and past star formation history, we argue that the extended, quiescent, gas disk associated with UGC 5288 is primordial in nature.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.