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

TL;DR

This paper presents the development and successful deployment of a new 100-GHz dual-beam sideband-separating SIS receiver for the NRO 45-m telescope, enabling advanced astronomical observations of high-redshift galaxies.

Contribution

The paper introduces a novel dual-beam, sideband-separating SIS receiver system operating at 100 GHz with improved noise performance and beam separation, tailored for high-redshift galaxy spectral line searches.

Findings

Successfully observed CO emission at z=2.56, validating the receiver's performance.

Achieved single-sideband noise temperature below 50 K across 80-116 GHz.

System noise temperature including atmosphere is 150-300 K at 97 GHz.

Abstract

We have developed a two-beam waveguide-type dual-polarization sideband-separating SIS receiver system in the 100-GHz band for {\it z}-machine on the 45-m radio telescope at the Nobeyama Radio Observatory. The receiver is intended for astronomical use in searching for highly redshifted spectral lines from galaxies of unknown redshift. This receiver has two beams, which have 45$^{\prime\prime}$ of beam separation and allow for observation with the switch in the on-on position. The receiver of each beam is composed of an ortho-mode transducer and two sideband-separating SIS mixers, which are both based on a waveguide technique, and the receiver has four intermediate frequency 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, and the image rejection ratios are greater than 10 dB in most of the same frequency range. The new receiver system has been installed in the telescope, and we successfully observed a $^{12}$CO ({\it J}=3--2) emission line toward a cloverleaf quasar at {\it z} = 2.56, which validates the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, is typically 150--300 K at a radio frequency of 97 GHz. We have begun blind search of high-{\it J} CO toward high-{\it z} submillimeter galaxies.