Star formation and AGN in the early universe: Quasars in the MAMBO Deep Field Survey

Blank field surveys with SCUBA and MAMBO revealed a population of (sub)mm background galaxies which are massive, similar to 10(11) M(circle dot) starbursts at median redshifts of similar to 2.5. Due to a radio-selection bias, for one third of the SCUBA/MAMBO sources a clear optical identification or redshift estimate has not yet been possible, but it is likely that these sources lie at redshifts > 3. We find evidence for a different population dominating the counts at S(1.2mm) > 10 mJy. The three brightest sources yet found in a wide field MAMBO survey are of lower redshifts (similar to 0.8 to 1.4), are X-ray bright, radio-loud, and time-variable. Their areal density is significantly higher than that expected from an extrapolation of the flat spectrum radio source population to 1.2 mm. Our preliminary analysis of the the brightest MAMBO source with a thermal submm spectrum (10 mJy at 1.2 mm) suggests it to be a radio-quiet, X-ray bright quasar at z similar to 3, thereby is possibly the most luminous starburst ever found.