Fueling the central engine of radio galaxies -: I.: The molecular/dusty disk of 4C 31.04

We report the detection of a massive (M-gas > 5 x 10(9) M.) molecular/dusty disk of 1.4 kpc-size fueling the central engine of the compact symmetric object (CSO) 4C 31.04, based on high-resolution (0.5"-1.2") observations done with the IRAM Plateau de Bure interferometer (PdBI). These observations allow us for the first time to detect and map the continuum emission from dust at 218 GHz in the disk of a CSO. The case for a massive disk is confirmed by detection of strong HCO+(1-0) line emission and absorption. The molecular gas mass of 4C 31.04 is in the range 0.5 x 10(10)-5 x 10(10) M.. While the distribution and kinematics of the gas roughly correspond to those of a rotating disk, we find evidence of distortions and non-circular motions that suggest the disk is not in a dynamically relaxed state. We discuss the implications of these results for the understanding of the evolution of radio galaxies.