A New 100-GHz Band Two-Beam Sideband-Separating SIS Receiver for Z-Machine on the NRO 45-m Radio Telescope

摘要

We have developed a two-beam waveguide-type dual-polarizationsideband-separating SIS receiver system in the 100-GHz band for {\it z}-machineon the 45-m radio telescope at the Nobeyama Radio Observatory. The receiver isintended for astronomical use in searching for highly redshifted spectral linesfrom galaxies of unknown redshift. This receiver has two beams, which have45$^{\prime\prime}$ of beam separation and allow for observation with theswitch in the on-on position. The receiver of each beam is composed of anortho-mode transducer and two sideband-separating SIS mixers, which are bothbased on a waveguide technique, and the receiver has four intermediatefrequency bands of 4.0--8.0 GHz. Over the radio frequency range of 80--116 GHz,the single-sideband receiver noise temperature is lower than about 50 K, andthe image rejection ratios are greater than 10 dB in most of the same frequencyrange. The new receiver system has been installed in the telescope, and wesuccessfully observed a $^{12}$CO ({\it J}=3--2) emission line toward acloverleaf quasar at {\it z} = 2.56, which validates the performance of thereceiver system. The SSB noise temperature of the system, including theatmosphere, is typically 150--300 K at a radio frequency of 97 GHz. We havebegun blind search of high-{\it J} CO toward high-{\it z} submillimetergalaxies.