CO (J=4 -> 3) and 650 micron continuum observations of the z=0.93 hyperluminous infrared galaxy FSC 15307+3252

We report the results of our CO J = 4 --> 3 line and rest-frame 650 mu m co ntinuum observations of the z = 0.93 hyperluminous infrared galaxy FSC 1530 7+3252 using the Owens Valley Millimeter Array. No line or continuum emissi on was detected, but the derived limits provide a useful constraint on the temperature, emissivity, and mass of the cold dust associated with FSC 1530 7+3252 and its molecular gas content. The 3 sigma upper limit on the velocity-integrated CO (4-3) line flux is 1. 6 Jy km s(-1) (for Delta V = 300 km s(-1)). This corresponds to a surprisin gly small total molecular gas mass limit of 5 x 10(9) h(-2) M. for this gal axy with infrared luminosity L-FIR > 10(13) L.. Combined with existing phot ometry data, our 3 sigma upper limit of 5.1 mJy for the 239 GHz (650 mu m r est wavelength) continuum flux yields a total dust mass of 0.4-1.5 times 10 (8) M.. The CO luminosity (thus molecular gas content) and the resulting ga s-to-dust ratio are lower than the values typical for the more gas-rich inf rared 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 Cygn us A. The far-infrared (FIR) luminosity to dust mass ratios, L-FIR/M-dust, for al l three galaxies hosting a powerful active galactic nucleus (FSC 10214+4724 , FSC 15307+3252, and Cygnus A) are larger than reasonably expected for a g alaxy dominated by a starburst and 4 times larger than Arp 220. Therefore t he bulk of the observed FIR luminosity in these galaxies is likely powered by their luminous active nuclei.