A 1.85-m mm-submm Telescope for Large-Scale Molecular Gas Surveys in 12CO, 13CO, and C18O (J = 2-1)

We have developed a new mm-submm telescope with a diameter of 1.85-m installed at the Nobeyama Radio Observatory. The scientific goal is to precisely reveal the physical properties of molecular clouds in the Milky Way Galaxy by obtaining a large-scale distribution of molecular gas, which can also be compared with large-scale observations at various wavelengths. The target frequency is ∼ 230 GHz; simultaneous observations at the molecular rotational lines of J = 2-1 of three carbon monoxide isotopes (¹²CO, ¹³CO, C¹⁸ O) are achieved with a beam size (HPBW) of 2.7'. In order to accomplish the simultaneous observations, we have developed waveguide-type sideband-separating SIS mixers to obtain spectra separately in the upper and lower side bands. A Fourier digital spectrometer with a 1 GHz bandwidth having 16384 channels is installed, and the bandwidth of the spectrometer is divided into three parts, corresponding to each of the three spectra; the IF system has been designed so as to inject these three lines into the spectrometer. A flexible observation system was created mainly in Python on Linux PCs, enabling effective OTF (On-The-Fly) scans for large-area mapping. The telescope is enclosed in a radome with a membrane covered to prevent any harmful effects of sunlight, strong wind, and precipitation in order to minimize errors in the telescope pointing, and to stabilize the receiver and the IF devices. From 2011 November, we started science operation, resulting in a large-scale survey of the Orion A/B clouds, Cygnus OB7, Galactic Plane, Taurus, and so on. We also updated the receiver system for dual-polarization observations.