A color analysis of the nicmos parallel image archive

We present a photometric analysis of all high Galactic latitude (/b/ > 20 d egrees) broadband parallel images taken by the Near-Infrared Camera and Mul ti-Object Spectrometer instrument of the Hubble Space Telescope during its initial lifetime in HST Cycle 7. These images, taken through the F110W and F160W filters, reach a mean 3 sigma limiting magnitude of approximately 22 in both bands, and cover a total area of approximately 92 arcmin(2). The re ddest of the 358 galaxies detected have F110W-F160W colors and F160W magnit udes consistent with being a combination of both dusty star-forming and evo lved early-type galaxies at 1 less than or similar to z less than or simila r to 2. The surface density of these galaxies is comparable to that of the population of extremely red objects (EROs) discovered in ground-based surve ys (similar to 100 deg(-2)), suggesting that EROs also represent a combinat ion of both galaxy types in this redshift range. Roughly 10% of the detecte d galaxies appear to be blue compact dwarf galaxies at z less than or simil ar to 1, a result consistent with studies of the HST Medium Deep Survey fie lds. The surface density of these objects down to a magnitude of 22 in F160 W is similar to 300 deg(-2). None of the 631 point sources detected have F1 10W-F160W colors matching those expected for quasi-stellar objects (QSOs) w hose continua have been significantly reddened by internal dust. Our data l imit the surface density of such QSOs to be less than or similar to 50 deg- 2 down to the mean limiting magnitudes of the sample images. Since the surf ace density of QSOs detected on the basis of ultraviolet excess in optical surveys to comparable depth is similar to 100 deg(-2,) this argues against the suggestion that dust-reddened QSOs compose the undetected majority of t he QSO population. The F110W-F160W color can also be used to identify unred dened QSOs at z greater than or similar to 8, but we find no such candidate s. This is consistent with the evidence that QSO space density declines sha rply at z greater than or similar to 5.