350 µm sharc-II imaging of luminous high-redshift radio galaxies

Abstract

Using the filled bolometer array SHARC-II on the Caltech Submillimeter Observatory (CSO), we have obtained deep (σ_(rms) ~ 15 mJy beam^(–1)), high-quality 350 µm maps of five of the most luminous high-z radio galaxies known. In all cases the central radio galaxy is detected at the ≳3σ level, and in some cases the high resolution of SHARC-II (FWHM = 9″) allows us to confirm the spatially extended nature of the dust emission. In PKS 1138–262 (z = 2.156), 8C 1909+722 (z = 3.538) and 4C 41.17 (z = 3.792), additional sources – first discovered by SCUBA at 850 µm and believed to be dusty, merging systems associated with the central radio galaxy – are detected at 350 µm. Furthermore, in PKS 1138 and 4C41.17 additional SHARC-II sources are seen which were not detected at 850 µm, although the reality of these sources will have to be confirmed by independent submm observations. Thus, our observations seem to support the notion of extended star formation taking place in radio galaxies at high redshifts, and that these systems sit at the centers of overdense regions harbouring a complexity of dusty and vigorously star forming systems. At the redshift of the radio galaxies, the 350 µm observations sample very close to the rest-frame dust peak (typically at ~100 µm), and they therefore contribute a particularly important point to the spectral energy distributions of these sources, which we use this in conjunction with existing (sub)millimeter data to derive FIR luminosities, dust temperatures and spectral emissivities of the central radio galaxies.