Caltech faint galaxy redshift survey. X. A redshift survey in the region of the Hubble Deep Field North

Judith G. Cohen, David W. Hogg, Roger Blandford, Lennox L. Cowie, Esther Hu, Antoinette Songaila, Patrick Shopbell, Kevin Richberg

    Research output: Contribution to journalArticlepeer-review


    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, ΩM = 0.3, ∧ = 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[(zphot - zspec)/(1 + zspec)] = 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.

    Original languageEnglish (US)
    Pages (from-to)29-52
    Number of pages24
    JournalAstrophysical Journal
    Issue number1 PART 1
    StatePublished - Jul 20 2000


    • Cosmology: observations
    • Galaxies: distances and redshifts
    • Galaxies: luminosity function, mass function
    • Surveys

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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