Photometric Redshifts and Morphologies of Galaxies in the NICMOS Parallel Fields

We present positions, magnitudes, sizes and morphological classifications for111 galaxies discovered in the Hubble Space Telescope NICMOS Camera 1 andCamera 2 parallel fields. We combine the magnitudes measured in the JHK-analogfilters with those from deep ground-based images in V and/or R to measurephotometric redshifts for 71 objects using Bruzual-Charlot population synthesismodels. We find that these objects fall in the range z ~ 0.0 - 2.7, with a meanredshift of 0.8 and a mean luminosity of 1.6 L*. The NICMOS images reveal manyof the objects to be ordered spirals and ellipticals similar to those in thelocal universe. However, we find a higher fraction (~ 14%) of morphologicallypeculiar and/or interacting galaxies than is observed among local galaxies (~3% - 4%). This is consistent with the results from other deep HST imagesincluding the Hubble Deep Field and Hubble Medium Deep Survey Field that thefraction of peculiar and interacting galaxies increases with redshift. As theNICMOS images of the sample galaxies cover their rest-frame near infrared andoptical emission, this result increases confidence that such changes inmorphology are genuine, as opposed to an effect produced by viewing galaxies inthe rest-frame ultraviolet. We also find that at least 26 of the samplegalaxies appear to be members of (non-interacting) pairs or groups, based ontheir proximity to one another and photometric redshifts. This is consistentwith the results of recent ground-based optical surveys covering larger areas,and with the detection of galaxy groups and filaments at redshifts higher thanthose covered by our sample.Comment: 36 pages, 7 figures, accepted for publication in The Astronomical Journa