The object, known as the Cloverleaf Quasar
(H1413+117), is interesting in several respects. The name derives from its optical image, which is split into four spots within about 1 arcsecond as a result of gravitational lensing, presumably by an intervening galaxy (as yet undetected). The Cloverleaf is also a Broad Absorption Line Quasar (BALQ), and may be a member of the subset of low-ionization, or Mg II, BALQs. We selected the Cloverleaf for CO studies because of its strong far-IR/submm flux, which we measured as part of a program to examine the submm cutoffs in the spectra of normal and BAL quasars. We found the observed submm continuum strength and shape of the Cloverleaf to be nearly identical to that of IRAS F10214+4724. Since CO line emission and far-IR/submm continuum flux are correlated it seemed that the Cloverleaf should be a good candidate for detectable CO emission. We have recently confirmed the Plateau de Bure CO(3-2) measurement, and detected other transitions of CO as well as CI, using the 30m telescope at Pico Veleta.
The lensing amplification factor is not known, but if it is not too large the inferred gas mass of the Cloverleaf is consistent with the dynamical mass, and with the total baryonic mass of L* galaxies today, suggesting that either the host galaxy is in a primitive state or its gas content has been greatly enhanced by mergers with other gas-rich systems.
We thank S. Guilloteau for scheduling the observations, and D. Downes for assistance with the data reduction.
Figure 2: CO J=3-2 (rest frequency 345.7 GHz) spectrum observed with the Plateau de Bure Interferometer. The velocity scale represents the offset relative to the central observed frequency of 97.134 GHz.