STScI Preprint #1252

Clustering at High Redshift: Precise Constraints from a Deep, Wide Area Survey

We present constraints on the evolution of large-scale structure from a catalog of 710,000 galaxies with I_AB 24 derived from a KPNO 4m CCD imaging survey of a contiguous 4^o × 4^o region. The advantage of using large contiguous surveys for measuring clustering properties on even modest angular scales is substantial: the effects of cosmic scatter are strongly suppressed. We provide highly accurate measurements of the two-point angular correlation function, (), as a function of magnitude on scales up to 1.5^o. The amplitude of () declines by a factor of ~ 10 over the range 16 I 20 but only by a factor of 2 - 3 over the range 20 < I 23. For a redshift dependence of the spatial correlation function, (r), parameterized as (r,z) = (r / r_o)^- (1 + z)^-(3+), we find r_o = 5.2±0.4 h^-1 Mpc, and 0 for I 20. This is in good agreement with the results from local redshift surveys. At I > 20, our best fit values shift towards lower r_o and more negative . A strong covariance between r_o and prevent us from rejecting > 0 even at faint magnitudes but if > 1, we strongly reject r_o 4h^-1 Mpc (co-moving). The above expression for (r,z) and our data give a correlation length of r_o(z = 0.5) 3.0±0.4h^-1 Mpc, about a factor of 2 larger than the correlation length at z = 0.5 derived from the Canada-France Redshift Survey (CFRS; Le Fevre et al. (1996)). The small volume sampled by the CFRS and other deep redshift probes, however, make these spatial surveys strongly susceptible to cosmic scatter and will tend to bias their derived correlation lengths low. Our results are consistent with redshift distributions in which ~30-50% of the galaxies at I = 23 lie at z > 1. The best fit power law slope of the correlation function remains independent of I magnitude for I 22. At fainter limits, there is a suggestive trend towards flatter slopes that occurs at fluxes consistent with similar trends seen by Neuschaffer & Windhorst (1995) and Campos et al. (1995). The galaxy counts span 11 magnitudes and provide an accurate calibration of the galaxy surface density. We find evidence for mild galaxy evolution - about 1 mag of brightening or a doubling of the density by I=23 relative to an _o = 1 no evolution model; about 0.5 mag of brightening or a factor of 1.5 increase in surface density relative to an open model. Our galaxy counts agree well with those from the HDF survey and, thus, argue against a significant inclusion of sub-galactic components in the latter census for I < 24.

Status:

Appeared in: The Astrophysical Journal, 506:33-44, 1998

Affiliations:

¹)Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218^(6)
2)National Optical Astronomy Observatories,Tucson, AZ 85726^(7)
3)University of Durham, Department of Physics,South Road, Durham, DH1 3LE, UK
⁴)Johns Hopkins University, Department of Physics & Astronomy,Baltimore, MD 21218
⁵) Visiting Astronomer Kitt Peak National Observatory, NOAO.
⁶) The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under National Aeronautical and Space Administration (NASA) Contract NAS5-26555.
⁷) The National Optical Astronomy Observatories are operated by AURA, Inc., under cooperative agreement with the National Science Foundation.