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Spectroscopic Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11

Daniel Stern·Brad Holden·S. A. Stanford·Hyron Spinrad
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Abstract

We report the discovery of a galaxy overdensity at z=1.11 associated with the z=1.110 high-redshift radio galaxy MG0442+0202. The group, CL0442+0202, was found in a near-infrared survey of z>1 radio galaxies undertaken to identify spatially-coincident regions with a high density of objects red in I-K' color, typical of z>1 elliptical galaxies. Spectroscopic observations from the Keck telescope reveal five galaxies within 35" of MG0442+0202 at 1.10 5e-16 erg/cm2/s. One of these point sources is identified with a radio-quiet, typeII quasar at z=1.863, akin to sources recently reported in deep Chandra surveys. The limit on an extended hot intracluster medium in the Chandra data is S(1-6keV) < 1.9e-15 erg/cm2/s (3-sigma, 30" radius aperture). Though the X-ray observations do not confirm the existence of a massive, bound cluster at z>1, the success of the optical/near-infrared targeting of early-type systems near the radio galaxy validates searches using radio galaxies as beacons for high-redshift large-scale structure. We interpret CL0442+0202 to be a massive cluster in the process of formation.

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Daniel Stern, Brad Holden, S. A. Stanford, Hyron Spinrad. 2003-06-09. Spectroscopic Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11. https://doi.org/10.1086/374229

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