Arecibo mapping of three extended H I galaxy disks and conjectures on what lies beyond

Details Arecibo mapping of three extended H I galaxy disks and conjectures on what lies beyond Arecibo mapping of three extended H I galaxy disks and conjectures on what lies beyond

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aj....106...39h&link_type=abstract

Astronomical Journal (ISSN 0004-6256), vol. 106, no. 1, p. 39-55.

Other

62

Disk Galaxies, Dwarf Galaxies, Galactic Rotation, H I Regions, Irregular Galaxies, Astronomical Observatories, Charge Coupled Devices, Computer Aided Mapping

Scientific paper

We present Arecibo H I mapping of three dwarf irregular galaxies with H II envelopes more than five times the diameter of their optically detectable stellar regions. These include one isolated system, DDO 154, and two systems that are apparently interacting tidally with a larger companion. DDO 137 and its companion NGC 4532 exhibit an enormous horseshoe-shaped cloud with quite complex kinematics. The H I around VCC 2062 appears on the surface to be a plume swept from NGC 4694 by tidal or ram-pressure mechanisms; however, the coincidence of a faint stellar patch with the peak H I column density bears striking resemblance to the 'protogalaxy' H I 1225+0146. Drawing on theoretical considerations and on the observation that DDO 154 and other extended disks appear to truncate abruptly at an H I column density around 2 x 10 exp 19/sq cm, we conjecture that the total hydrogen column density declines more slowly than exponentially beyond that point. Extended partially ionized disks may then account for recently reported 1ow-redshift Ly-alpha absorption features.

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