DUST IN HIGH-Z RADIO-LOUD AGN

We present continuum observations of a small sample of high-redshift, radio-loud AGN (radio galaxies and quasars) aimed at the detection of thermal emission from dust. Seven AGN were observed with IRAM and SEST at 1.25 mm; two of them, the radio galaxies 1243+036 (z similar to 3. 6) and MG 1019+0535 (z similar to 2.8) were also observed at 0.8 mm wi th the JCMT submillimetre telescope. Additional VLA observations were obtained in order to derive the spectral shape of the synchrotron radi ation of MG 1019+0535 at high radio frequencies. MG 1019+0535 and TX 0 211-122 were expected to contain a large amount of dust based on their depleted Ly alpha emission. The observations suggest a clear 1.25-mm flux density excess over the synchrotron radiation spectrum of MG 1019 +0535, suggesting the presence of thermal emission from dust in this r adio galaxy, whereas the observations of TX 0211-122 were not sensitiv e enough to meaningfully constrain its dust content. On the other hand , our observations of 1243+036 provide a stringent upper limit on the total dust mass of < 10(8) M.. Finally, we find that the spectra of th e radio-loud quasars in our sample (2 < z < 4.5) steepen between rest- frame radio and the far-infrared. We discuss the main implications of our results, concentrating on the dusty radio galaxy, MG 1019+0535.