Resolved HI Disks
Extended Gas Disks Around Galaxies
My primary area of research (i.e., PhD thesis work) is on galaxies that possess HI disks that extend far beyond the optical disk. A classic example of this is UGC 5288 whose HI to optical radii ratio is about ten. Explanations for these disk range from them being the remnants of the protogalacitc cloud from which the host galaxy collapsed to gas that was expelled by a major star formation event. Despite galaxy such as UGC 5288 begin know for more than 30 years, little work as been done to establish the nature of these disks. The primary reason for this is that too few systems are know to carry a proper survey of their properties. The ALFALFA (Arecibo Legacy Fast ALFA) survey will be able to change this. Catalog estimates of systems resolved by the ALFA beam number around 100 and include both normal galaxies with large HI disks as well as those systems with the unusually extended HI that I am interested. A sample of this size will allow me to combine the HI data with optical information on galaxy colors and Hα emission to begin to pin down how these systems came about and look for any correlation between morphology and extended disk, environment and extended disk, etc.
Deconvolution Routine for ALFALFA
Although the ALFALFA data are ideal for studying extended gas disks, the complicated sidelobe structure is not. The above figure gives an example of the typical beam pattern found in the ALFALFA data cubes. In order for HI sizes to be measured, the sidelobe artifacts need to be removed via deconvolution.
To accomplish this I have written a CLEAN-like deconvolution routine for the ALFALFA data. The beam is modeled by simulating the observation of a theoretical point source using the actual ALFALFA drift settings and gridding method. An example of the routine in action on a continuum source can be seen above. More information about the routine can be found here.
Connections with Lyman-α Systems
Since my thesis will find both galaxies with normal and unusually extended HI, it is possible to study how the distribution of gas disk sizes at z~0 relate to Lyman-α and Damped Lyman-α systems at higher redshifts.
An Google Sky View of Unusually Extended Galaxies
This provides a graphically-rich view of the seven galaxies with unusually extended HI gas (DHI/Doptical > 5) using Google Sky and the Google Maps API.
Interactive View