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Published July 20, 2000 | Published
Journal Article Open

Caltech Faint Galaxy Redshift Survey. X. A Redshift Survey in the Region of the Hubble Deep Field North


A redshift survey has been carried out in the region of the Hubble Deep Field North using the Low Resolution Imaging Spectrograph (LRIS) at the Keck Observatory. The resulting redshift catalog, which contains 671 entries, is a compendium of our own data together with published LRIS/Keck data. It is more than 92% complete for objects, irrespective of morphology, to R = 24 mag in the HDF itself and to R = 23 mag in the flanking fields within a diameter of 8' centered on the HDF, an unusually high completion for a magnitude-limited survey performed with a large telescope. A median redshift z = 1.0 is reached at R ~ 23.8. Strong peaks in the redshift distribution, which arise when a group or poor cluster of galaxies intersect the area surveyed, can be identified to z ~ 1.2 in this data set. More than 68% of the galaxies are members of these redshift peaks. In a few cases, closely spaced peaks in z can be resolved into separate groups of galaxies that can be distinguished in both velocity and location on the sky. The radial separation of these peaks in the pencil-beam survey is consistent with a characteristic length scale for the their separation of ≈70 Mpc in our adopted cosmology (h = 0.6, Ω_M = 0.3, Λ = 0). Strong galaxy clustering is in evidence at all epochs back to z ≤ 1.1. A near-infrared selected sample with K < 20 was also constructed in this field. Extremely red objects with R-K > 5.0 comprise 7% of the total K-selected sample. This fraction rises rapidly toward fainter K magnitude, reaching about 10% at K ~ 19.7. We have attempted to identify the radio sources in the region of the HDF. The secure radio sources seem to divide into two classes. The first have reasonably bright galaxies at moderate redshifts as optical counterparts, while the second, comprising about 1/3 of the total, have extremely faint optical counterparts (R ≥ 25 mag). These do not represent a continuous extrapolation in any property (z or dust content) of the first group. We identify ~2/3 of the secure mid-IR sources in the region of the HDF with normal galaxies with z < 1.3. The ratio of the mid-IR to optical flux increases as z increases, but this is due primarily to selection effects, and the same trend is seen in the radio sources. We suggest that the mid-IR emission is more tightly coupled to the rate of ongoing star formation than is the radio emission. We also demonstrate that the best photometric redshift techniques are capable of reaching a precision of σ[(z_(phot) - z_(spec))/(1 + z_(spec))] = 0.05 for the majority of galaxies with z < 1.3. The two broad-lined AGNs with z < 3 are the brightest objects in the redshift peak at z ~ 0.96.

Additional Information

© 2000. The American Astronomical Society. Received 1999 June 21; accepted 1999 December 2. Based in large part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California. The entire Keck/LRIS user community owes a huge debt to Jerry Nelson, Gerry Smith, Bev Oke, and many other people who have worked to make the Keck Telescope and LRIS a reality. We are grateful to the W. M. Keck Foundation, and particularly its late president, Howard Keck, for the vision to fund the construction of the W. M. Keck Observatory. We are very grateful to A. Phillips and other members of the Lick Deep Group for permission to examine their spectra of objects in the region of the HDF and for their cooperation in resolving problem cases. We are also very grateful Brad Behr for help in constructing Figures 2 and 3. J. G. C. is grateful for the hospitality of Princeton University, and R. D. B. and J. G. C. are grateful for the hospitality of the Institute for Advanced Study. J. G. C. is grateful for partial support from STScI/NASA grant AR-06337.12-94A. R. D. B. acknowledges support under NSF grant AST 95-29170. D. W. H. was supported in part by a Hubble Fellowship grant HF-01093.01-97A from STScI (which is operated by AURA under NASA contract NAS5-26555). K. R. is grateful to the Caltech SURF program for partial support.

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