Observations of Fsc

We report the results of our CO J \ 4 ] 3 line and rest-frame 650 km continuum observations of the z\ 0.93 hyperluminous infrared galaxy FSC 15307]3252 using the Owens Valley Millimeter Array. No line or continuum emission was detected, but the derived limits provide a useful constraint on the temperature, emissivity, and mass of the cold dust associated with FSC 15307]3252 and its molecular gas content. The 3 p upper limit on the velocity-integrated CO (4È3) line Ñux is 1.6 Jy km s~1 (for *V \ 300 km s~1). This corresponds to a surprisingly small total molecular gas mass limit of 5 ] 109 h~2 for this M _ galaxy with infrared luminosity Combined with existing photometry data, our 3 p upper L FIR [ 1013 L _ limit of 5.1 mJy for the 239 GHz (650 km rest wavelength) continuum Ñux yields a total dust mass of 0.4È1.5 times 108 The CO luminosity (thus molecular gas content) and the resulting gas-to-dust M _ . ratio are lower than the values typical for the more gas-rich infrared galaxies, but they are within the observed ranges. On the other hand, FSC 15307]3252 has a dust content and infrared luminosity 40 and 200 times larger than the infrared bright elliptical-like galaxies NGC 1275 and Cygnus A. The far-infrared (FIR) luminosity to dust mass ratios, for all three galaxies hosting a L FIR/Mdust, powerful active galactic nucleus (FSC 10214]4724, FSC 15307]3252, and Cygnus A) are larger than reasonably expected for a galaxy dominated by a starburst and 4 times larger than Arp 220. Therefore the bulk of the observed FIR luminosity in these galaxies is likely powered by their luminous active nuclei. Subject headings : dust, extinction È galaxies : active È galaxies : formation È galaxies : individual (FSC 15307]3252) È infrared : galaxies È ISM: molecules