| Description |
Our Herschel key project The Dusty Young Universe observed 71 quasars at the highest redshifts (z > 5) with PACS and SPIRE. Similar to the local universe we find that the hottest, AGN heated dust shows a flat or slightly rising spectral energy distribution in nuF_nu between 24mu (Spitzer) and PACS 100mu (i.e. rest-frame 3.4mu < lambda_rest < 14mu at z=6). However, in the course of the project we identified some exceptional cases that are undetected by PACS at 100mu. Their upper limits result in nuF_nu(100mu) < 0.8*nuF_nu(24mu) indicating a deficit of cooler dust below T virgul 300 K. Such cases are not known among AGN in the local universe and seem to require a very compact central dust distribution. Here we propose to re-observe the best six of these exceptional quasars with PACS at 100 and 160mu with a threefold integration time in order to reach a factor of 2 deeper in flux when combining with the already acquired data. Both a successful detection or a substantially lowered upper limit will allow us to determine the temperature of the hot dust better and estimate its total mass. The small radius of the dust distribution might indicate dust production near the quasar core. PACS on Herschel is the unique facility to investigate the apparent differences of the dust distributions in quasars between the young universe and today. |
