Photometric redshifts and morphologies of galaxies in the NICMOS parallel fields

We present positions, magnitudes, sizes, and morphological classifications for 111 galaxies discovered in the Hubble Space Telescope NICMOS camera 1 a nd camera 2 parallel fields. We combine the magnitudes measured in the JHK- analog filters with those from deep ground-based images in V and/or R to me asure photometric redshifts for 71 objects using Bruzual & Chariot populati on synthesis models. We find that these objects fall in the range z similar to 0.0-2.7, with < z > congruent to 0.8 and a mean luminosity < L > congru ent to 1.6L*. The NICMOS images reveal many of the galaxies to be ordered s pirals and ellipticals similar to those in the local universe, with a high degree of symmetry and brightness profiles that are well fitted by de Vauco uleurs's r(1/4) and exponential disk laws. However, we find a higher fracti on (similar to 14%) of morphologically peculiar and/or interacting galaxies in the sample than is observed among local galaxies (similar to 3%-4%). Th is is consistent with the result from other deep HST images including the H ubble Deep Field and Hubble Medium Deep Survey field that the fraction of p eculiar and interacting galaxies increases with redshift. As the NICMOS ima ges of the sample galaxies cover their rest-frame near-infrared and optical emission, this result increases confidence that such changes in morphology are genuine, as opposed to an effect produced by viewing galaxies in the r est-frame ultraviolet. We also End that at least 26 of the sample galaxies appear to be members of (noninteracting) pairs or groups, based on their pr omixity to one another and photometric redshifts. This is consistent with t he results of recent groundbased optical surveys for faint galaxies coverin g larger areas and with the detection of galaxy groups and filaments at red shifts higher than those covered by the present sample.