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Morphology and surface brightness evolution of z∼1.1 radio galaxies |
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| Authors: | Nathan Roche Stephen Eales & Steve Rawlings |
| Institution: | Department of Physics and Astronomy, University of Cardiff, PO Box 913, Cardiff CF2 3YB,;Department of Astrophysics, University of Oxford, Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH |
| Abstract: | We use K '-band (2.1-μm) imaging to investigate the angular size and morphology of 10 6C radio galaxies, at redshifts 1≤ z ≤1.4. Two radio galaxies appear to be undergoing mergers, another contains, within a single envelope, two intensity peaks aligned with the radio jets, while the other seven appear consistent with being normal ellipticals in the K band. Intrinsic half-light radii are estimated from the areas of each radio galaxy image above a series of thresholds. The 6C galaxy radii are found to be significantly smaller than those of the more radio-luminous 3CR galaxies at similar redshifts. This would indicate that the higher mean K -band luminosity of the 3CR galaxies reflects a difference in the size of the host galaxies, and not solely a difference in the power of the active nuclei. The size–luminosity relation of the z ～1.1 6C galaxies indicates a 1.0–1.6 mag enhancement of their rest frame R -band surface brightness relative to either local ellipticals of the same size or FRII radio galaxies at z <0.2. The 3CR galaxies at z ～1.1 show a comparable enhancement in surface brightness. The mean radius of the 6C galaxies suggests that they evolve into ellipticals of L ～ L * luminosity, and is consistent with their low-redshift counterparts being relatively small FRII galaxies ～25 times lower in radio luminosity, or small FRI galaxies ～1000 times lower in radio luminosity. Hence the 6C radio galaxies appear to undergo as much optical and radio evolution as the 3CR galaxies. |
| Keywords: | galaxies: active galaxies: evolution galaxies: photometry radio continuum: galaxies |