Extremely Red Objects from the Hubble Space Telescope NICMOS Parallel Imaging Survey

August 2000 • 2000AJ....120..575Y

Authors • Yan, Lin • McCarthy, Patrick J. • Weymann, Ray J. • Malkan, Matthew A. • Teplitz, Harry I. • Storrie-Lombardi, Lisa J. • Smith, Malcolm • Dressler, Alan

Abstract • We present a catalog of extremely red objects (EROs) discovered using the Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) parallel imaging database and ground-based optical follow-up observations. Within an area of 16 arcmin², we detect 15 objects with R-F160W>5 and F160W<21.5. We have also obtained K-band photometry for a subset of the 15 EROs. All of the R-F160W selected EROs imaged at K-band have R-K>6. Our objects have F110W-F160W colors in the range 1.3-2.1, redder than the cluster elliptical galaxies at z~0.8 and nearly 1 mag redder than the average population selected from the F160W images at the same depth. In addition, among only 22 NICMOS pointings, we detected two groups or clusters in two fields; each contains three or more EROs, suggesting that extremely red galaxies may be strongly clustered. At bright magnitudes with F160W<19.5, the ERO surface density is similar to what has been measured by other surveys. At the limit of our sample, F160W=21.5, our measured surface density is 0.94+/-0.24 arcmin^-2. Excluding the two possible groups or clusters and the one apparently stellar object reduces the surface density to 0.38+/-0.15 arcmin^-2.

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Harry Teplitz

Senior Scientist