1999A&A...349..363G

We report the results of a systematic search for redshifted rotational lines of CO and dust emission towards a sample of 9 high redshift radio quiet quasars using the IRAM Plateau de Bure interferometer. Dust emission at ∼1.35 mm has been found in 5 out of the 9 objects. These results confirm the corresponding previous detections with the MPIfR bolometer at the 30-m. No 3mm continuum was detected in any source. The flux densities measured at 1.35 mm with the interferometer are systematically smaller by ∼30% from the broad-band bolometer fluxes, consistent with an average spectral index of ∼3.5 within the calibration uncertainty. In parallel, searches for CO in significant redshift ranges were performed for 8 of the above sources. 6 sources were not detected. Assuming a line width of ≤450km/s, we obtain typical upper limits of ∼0.4-0.5Jy.km/s at the 3σ level in the frequency (redshift) range searched. We report a tentative (3σ) detection of the J=3-2 line of CO in Q 1230+1627B, and a unambigous detection of the J=5-4 CO line in the gravitationally lensed radio quiet quasar BRI 0952-0115 at a redshift of z=4.43. After BR 1202-0725 at z=4.69 (Otha et al. 1996, Omont et al. 1996a), and BRI 1335-0417 at z=4.41 (Guilloteau et al., 1997A&A...328L...1G), this is the third detection of CO at z>4. The velocity-integrated CO(5-4) line flux is 0.91±0.11Jy.km/s, with a linewidth of 230±30km/s. The 1.35mm (250µm rest wavelength) dust continuum flux density is 2.23±0.51mJy, in agreement with previous measurements at 1.25mm at the 30-m IRAM telescope. The ratio of the CO to 1.35mm continuum flux is comparable to that of BRI 1335-0417 and 2-3 times larger than for BR 1202-0725. The angular resolution of the observation is not high enough to give evidence of any extension of the 1.35mm continuum and 3mm CO emission.