The clustering of K∼20 galaxies in 17 radio galaxy fields |
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Authors: | Nathan Roche Steve Eales & Hans Hippelein |
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Institution: | Department of Physics and Astronomy, University of Wales Cardiff, PO Box 913, Cardiff CF2 3YB,;Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany |
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Abstract: | We investigate the angular correlation function, ο(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 ο(θ) amplitude similar to that estimated by Carlberg et al. at K =21.5. The ο(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 ο(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 ο(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. |
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Keywords: | galaxies: clusters: general infrared: galaxies |
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