Deciphering the nature of unusually extended galactic HI disks

Details Deciphering the nature of unusually extended galactic HI disks Deciphering the nature of unusually extended galactic HI disks

Nov 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010phdt.......102d&link_type=abstract

ProQuest Dissertations And Theses; Thesis (Ph.D.)--Indiana University, 2010.; Publication Number: AAT 3423586; ISBN: 97811242462

Physics

3

Scientific paper

Unusually extended neutral gas disks have been found in both spiral and irregular galaxies. For these galaxies, the extent of the HI is unusual in the sense that "normal" galaxies have HI-to-optical diameter ratios of approximately two (Broeils & Rhee 1997), whereas these galaxies have ratios that often exceed five. These galaxies are also unusual in the sense that the typical explanation of an extended disk, i.e., a tidal interaction, is not likely because the majority of these systems are isolated. Prior to this work, few such systems were known since most were discovered serendipitously. In addition to furthering our understanding of the galaxy formation process, these extended galaxies are also important to our understanding of Damped Lyalpha (DLA) systems through their potential to connect apparently isolated DLA systems to galaxies. In order to characterize the properties of galaxies that harbor extended gas disks, gain insight into the origins of these systems, and understand their connection to DLA systems, the Arecibo Legacy Fast ALFA survey (ALFALFA; Giovanelli et al. 2005) was used to create an unbiased radio-selected sample of all galaxies with HI diameters larger than 3.5'. This approach provided a statistically significant sample of galaxies with both normal and unusual gas distributions. In addition to sample selection, the ALFALFA data were also used to characterize the bulk HI properties and kinematics. From these data, a HI diameter function was constructed and the typical extents of galaxies at column densities relevant for Lyalpha absorption were examined. By combining the ALFALFA data with optical broadband and narrowband imaging and higher resolution VLA maps, it was found that the key to understanding the origins and nature of unusually extended galactic gas disks lies in their specific angular momentum.

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