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A.N. Straughn, R.E. Ryan, S.H. Cohen, N.P. Hathi, R.A. Windhorst (Arizona State University), A. Pasquali (Institute of Astronomy, Zurich)
The Hubble Ultra Deep Field presents a wealth of galaxies, some very oddly shaped. In particular, we notice many galaxies that appear to have a bright knot at one end with an extended tail at the other. These “tadpole galaxies”—which are presumably in a dynamically unrelaxed state—are systematically selected from the UDF and studied as a function of their photometric redshift. Automatic selection is performed by creating two source catalogs with SExtractor—one catalog of pointlike objects (the knots) and the other catalog of extended sources (the tails). Ellipticity limits are imposed, and a new set of objects are selected from the above catalogs in which the knots and tails are within a certain distance of each other, corresponding to related objects on the image. Position angles of the objects are also used as a selection criterion, and the resulting catalog contains the desired set of tadpoles. It is found that in general the redshift distribution of these tadpole galaxies follows the distribution of all the galaxies in the field, ~10,000 total.
We discuss selection techniques in more detail, as well as morphological analysis and photometric redshift determination. The result that these galaxies are dynamically unrelaxed systems that have recently undergone merging activity is discussed.
This research was supported in part by the NASA Space Grant Graduate Fellowship at Arizona State University, HST Grant GO.9793.O* , and JWST Grant NAG 5-12460.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.