The clustering of K 20 galaxies in 17 radio galaxy fields

Abstract

We investigate the angular correlation function, ω(θ), of the galaxies detected in the 2.1-μm K′ band in 17 fields (101.5 arcmin2 in total), each containing a z∼1.1 radio galaxy. There is a significant detection of galaxy clustering at a limit of K∼20, with a ω(θ) amplitude similar to that estimated by Carlberg et al. at K=21.5. The ω(θ) amplitudes of these K-limited samples are higher than expected from the faint galaxy clustering in the blue and red passbands, but consistent with a pure luminosity evolution model if clustering is stable (ϵ=0) and the correlation function of early-type galaxies is steeper than that of spirals. We do not detect a significant cross-correlation between the radio galaxies and the other galaxies in these fields. The upper limits on the cross-correlation are consistent with a mean clustering environment of Abell class 0 for z∼1.1 radio galaxies, similar to that observed for radio galaxies at z∼0.5, but would argue against an Abell class 1 or richer environment. As Abell 0 clustering around the radio galaxies would not significantly increase the ω(θ) amplitude of galaxies in these fields, stable clustering with a steep ξ(r) for E/S0 galaxies appears to remain the most likely interpretation of the ω(θ) amplitude. At K≤20, the number of galaxy-galaxy pairs of 2–3 arcsec separation exceeds the random expectation by a factor of 2.15±0.26. The excess of close pairs is comparable to that previously reported for R-band data, and consistent with a ∼(1+z)2 evolution of the galaxy merger rate.