An ultra wide-band, high-sensitivity Q-band receiver for single-dish telescopes, eQ: Rest-frequency determination of CCS (JN = 43–32) and SO (JN = 10–01) and high-redshift CO (J = 1–0) detection.

This article reports on the development, installation, and commissioning of the eQ (extended Q-band) receiver, a new dual-linear polarization Q-band receiver covering 30–50 GHz with a low receiver noise temperature (~15 K), installed on the Nobeyama 45 m telescope. The eQ receiver offers the widest bandwidth and highest sensitivity among comparable large single-dish Q-band receivers, enabling simultaneous observations of multiple molecular transitions, including key Zeeman lines of CCS and SO for magnetic field measurements in dense molecular clouds, astrochemical studies, and detection of molecular lines from high-redshift galaxies. The authors refined the rest frequencies of CCS (J_N = 4_3–3_2) and SO (J_N = 1_0–0_1) transitions using simultaneous observations, determining values of 45.379033 GHz and 30.001542 GHz, respectively, with CCS (J_N = 3_2–2_1) at 33.751370 GHz as a reference. Mapping observations of the Taurus Molecular Cloud-1 (TMC-1) revealed spatial differentiation between SO and carbon-chain molecules, interpreted as evidence of shock-enhanced SO abundance linked to gravitational infall in a magnetically supercritical filament. Additionally, the eQ receiver successfully detected faint CO (J = 1–0) emission from a high-redshift (z = 2.442) galaxy, demonstrating its capability for extragalactic molecular line studies. The smoothed bandpass calibration (SBC) technique was also shown to reduce total observation time by a factor of about 2.5 compared to standard methods.