CO (J = 4 --> 3) and 650 Micron Continuum Observations of z=0.93   Hyperluminous Infrared Galaxy FSC 15307+3252
  We report the results of our CO J = 4 --> 3 line and rest frame 650 micron 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 sigma upper limit on the velocity integrated CO (4-3) line flux is 1.6 Jy km/s (for 300 km/s line width). This corresponds to a surprisingly small total molecular gas mass limit of 5 x 10^9 h^{-2} solar mass for this galaxy with infrared luminosity L(FIR) > 10^{13} solar luminosity. Combined with existing photometry data, our 3 sigma upper limit of 5.1 mJy for the 239 GHz (650 micron rest wavelength) continuum flux yields a total dust mass of 0.4-1.5 times 10^8 solar mass. The CO luminosity (thus molecular gas content) and the resulting gas-to-dust 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 FIR luminosity to dust mass ratios, L(FIR)/M(dust), for all three galaxies hosting a powerful AGN (FSC 10214+4724, FSC 15307+3252, Cygnus A) are larger than reasonably expected for a galaxy dominated by a starburst and four times larger than Arp 220. Therefore the bulk of the observe FIR luminosity in these galaxies is likely powered by their luminous active nucleus. 
M. S. Yun (NRAO) and N. Z. Scoville (Caltech)