A Search for CO Emission in High-Redshift Powerful Radio Galaxies

Upper limits for the molecular gas mass of 11 high-redshift (1 <z <4) powerful radio galaxies (HzPRGs) are presented. These observations include some of the most sensitive extragalactic CO observations to date. The four best-studied radio galaxies (3C 368, 4C 23.56, B2 0902+34, and 4C 41.17) have less than one-third the CO luminosity of the hyperluminous infrared galaxy IRAS F10214+4724, and, assuming a Galactic CO-to-H2 ratio, they have molecular gas masses comparable to or less than the most gas-rich, ultraluminous infrared galaxies (ULIGs) in the local (z ≤ 0.3) universe [i.e., M(H2) < 2-3 × 1010 h-2Msun; H0 = 100 h km s-1 Mpc-1 and q0 = 0.5]. Spectral energy distributions of eight HzPRGs show them to have UV-to-optical luminosities ranging from a factor of 0.1 to 1.0 that of the UV-to-optical luminosity of F 10214+4724. Recent submillimeter observations of three HzPRGs suggest that one source, 4C 41.17, may have an intense submillimeter-to-far-infrared excess. However, IRAS observations suggest that HzPRGs as a class are not hyperluminous at far-infrared wavelengths. We also consider how the possibility that F10214+4724 is a gravitationally lensed galaxy affects our interpretation of the data, as well as what it may mean for gas-rich galaxies in general.