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

Creators: 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 arcmin^2, 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).

Additional Information

© 2000. The American Astronomical Society. Received 2000 January 19; accepted 2000 March 14. We thank the staff of the Space Telescope Science Institute (STScI) for their efforts in making this parallel program possible. In particular, we thank Duccio Machetto, Peg Stanley, Doug van Orsow, and the staff of the PRESTO division. We also thank John Mackenty and members of the STScI NICMOS group for crafting the exposure sequences. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research was supported, in part, by grants from the Space Telescope Science Institute, GO-7499.01-96A, AR-07972.01-96A, and PO423101. H. I. T. acknowledges funding by the Space Telescope Imaging Spectrograph Instrument Definition Team through the National Optical Astronomy Observatories and by the NASA Goddard Space Flight Center.

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