The Hubble Ultra Deep Field with NICMOS

Summary

The Advanced Camera for Surveys (ACS) observations of the Hubble Ultra Deep Field (HUDF) provide the highest sensitivity optical observations of galaxies and stars ever achieved. The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) observations in the central portion of the field extend the wavelength coverage by a factor of two to beyond 1.6 microns. Although not as sensitive as the ACS images due to a much smaller field and less observing time, the NICMOS observations extend the redshift range of the HUDF to redshifts as high as 13. Even though the observations are sensitive to redshift 13 objects, we confine our investigation to objects between redshifts of 7 and 9 where there is flux in both the F110W and F160W bands. Candidate sources in this redshift region are identified by requiring a non-detection in the ACS bands and a detection in both the F110W and F160W bands. All of the candidates have an almost flat or blue color in the F110W and F160W bands. The extremely high sensitivity of the ACS observations make this a very stringent criterion. We identify five candidates for objects in this redshift range and discuss tests of the reality of these sources. Although the sources are selected to have flux in both NICMOS bands and none in the ACS bands, we also present the results of a photometric redshift analysis of the candidates. This shows them to be very blue galaxies with redshifts between 7.3 and 7.9. One source yielded an anomalous redshift and spectral type due to flux from an adjacent galaxy falling in the photometric aperture.