Wide-field mid-infrared and millimetre imaging of the high-redshift radio galaxy, 4C41.17

Abstract

We present deep 350- and 1200-micron imaging of the region around 4C41.17 -- 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-micron, as are two nearby 850-micron-selected galaxies; a third 850-micron source is detected at 350-micron and coincides with a ~ 2-sigma feature in the 1200-micron map. Further away from the radio galaxy an additional nine sources are detected at 1200-micron, bringing the total number of detected (sub)millimeter selected galaxies (SMGs) in this field to 14. Using radio images from the Very Large Array (VLA) and Spitzer mid-infrared (mid-IR) data, we find statistically robust radio and/or 24-micron counterparts to eight of the 14 SMGs in the field around 4C41.17. Follow-up spectroscopy with Keck/LRIS has yielded redshifts for three of the eight robustly identified SMGs, placing them in the redshift range 0.5 < z < 2.7, i.e. well below that of 4C41.17. We infer photometric redshifts for a further four sources using their 1.6-micron (rest-frame) stellar feature as probed by the IRAC bands; only one of them is likely to be at the same redshift as 4C41.17. Thus at least four, and as many as seven, of the SMGs within the 4C41.17 field are physically unrelated to the radio galaxy. With the redshift information at hand we are able to constrain the observed over-densities of SMGs within radial bins stretching to R=50 and 100" (~ 0.4 and ~ 0.8Mpc at z ~ 3.8) from the radio galaxy to ~ 5x and ~ 2x that of the field, dropping off to the background value at R=150". [Abridged]