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Wide-field mid-infrared and millimetre imaging of the high-redshift radio galaxy, 4C 41.17




We present deep 350- and 1200-μm imaging of the region around 4C 41.17 – one of the most-distant (z= 3.792) and luminous known radio galaxies – obtained with the Submillimeter High Angular Resolution Camera (SHARC-II) and the Max Planck Millimeter Bolometer Array (MAMBO). The radio galaxy is robustly detected at 350 and 1200 μm, as are two nearby 850-μm-selected galaxies; a third 850-μm source is detected at 350 μm and coincides with a ∼2σ feature in the 1200-μm map. Farther away from the radio galaxy additional nine sources are detected at 1200 μm, bringing the total number of detected (sub)millimetre-selected galaxies (SMGs) in this field to 14. Using radio images from the Very Large Array and Spitzer mid-infrared data, we find statistically robust radio and/or 24-μm counterparts to eight out of the 14 SMGs in the field around 4C 41.17. Follow-up spectroscopy with Keck/Low-Resolution and Imaging Spectrograph (LRIS) has yielded redshifts for three out of the eight robustly identified SMGs, placing them in the redshift range 0.5 ≲z≲ 2.7 that is well below that of 4C 41.17. We infer photometric redshifts for a further four sources using their 1.6-μm (rest-frame) stellar feature as probed by the IRAC bands; only one of them is likely to be at the same redshift as 4C 41.17. Thus at least four, and as many as seven, of the SMGs within the 4C 41.17 field are physically unrelated to the radio galaxy. With the redshift information at hand, we are able to constrain the observed overdensities of SMGs within radial bins stretching to R= 50 and 100 arcsec (∼0.4 and ∼0.8 Mpc at z≃ 3.8) from the radio galaxy to approximately five times and two times that of the field, dropping off to the background value at R= 150 arcsec. We thus confirm that 4C 41.17 resides in an overdense region of the Universe, but we have only been able to identify SMGs along the line of sight to the radio galaxy, typical of the blank-field SMG population. Finally, we report on the discovery of an extremely extended (∼110 kpc) Lyα blob at z= 2.672 associated with the brightest 1200-μm source in the field.

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