Galaxies in the Hubble Ultra Deep Field: I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology

We present aperture-matched PSF-corrected BV izJH photometry and Bayesian photometric redshifts (BPZ) for objects detected in the Hubble Ultra Deep Field (UDF), 8,042 of which are detected at the 10-σ level (e.g., i < 29.01 or z < 28.43). Most of our objects are defined identically to those in the public STScI catalogs, enabling straightforward object-by-object comparison. We have combined detections from i, z, J+H , and B+V+i+z images into a single comprehensive segmentation map. Using a new program called SExSeg we are able to force this segmentation map into SExtractor for photometric analysis. The resulting photometry is corrected for the wider NIC3 PSFs using our ColorPro software. We also correct for the ACS z-band PSF halo. Offsets are applied to our NIC3 magnitudes, which are found to be too faint relative to the ACS fluxes. Based on BPZ SED fits to objects of known spectroscopic redshift, we derived corrections of −0.30 ± 0.03 mag in J and −0.18 ± 0.04 mag in H . Our offsets appear to be supported by a recent recalibration of the UDF NIC3 images combined with non-linearity measured in NICMOS itself. The UDF reveals a large population of faint blue galaxies (presumably young starbursts), bluer than those observed in the original Hubble Deep Fields (HDF). Johns Hopkins University, Dept. of Physics & Astronomy, 3400 N. Charles St., Baltimore, MD 21218, USA Instituto de Astrof́isica de Andalućia (CSIC), Camino Bajo de Huétor 50, Granada 18008, Spain Calar Alto Observatory, Almeŕia E-040004, Spain University of California, Astronomy Dept., Santa Cruz, CA 95064