Faintest Galaxy Morphologies From HST WFPC2 Imaging of the Hawaii Survey Fields

Abstract

We present very deep HST WFPC2 images in the F814W filter of two Hawaii Survey fields, SSA13 and SSA22. Using these data with previous ground- based imaging and spectroscopy, we compare the colors, star-forming properties, and morphologies of the faintest galaxies with a reference sample of bright nearby galaxies and analyze the changes in field galaxy morphology with magnitude. Our principal result is the identification of a new morphological class of "chain" galaxies at the faintest magnitudes. Based on limited spectroscopy, we tentatively conclude that these are linearly organized giant star-forming regions at z = 0.5-3 and, if this is correct, that these are large galaxies in the process of formation.