The LMT 2 Millimeter Receiver System (B4R). I. Overview and Results of Science Demonstration

TL;DR

The paper reports on the successful deployment and testing of the B4R 2 mm receiver system on the LMT, demonstrating its capabilities for high-redshift galaxy spectroscopy and astrochemistry, with performance metrics aligning with design expectations.

Contribution

This work introduces the B4R receiver system for the LMT, enabling new science cases and demonstrating its performance through on-sky tests and observations.

Findings

Successful on-the-fly mapping and position-switching observations.

Aperture efficiencies consistent with design expectations.

Enabling sensitive 2 mm spectroscopic observations with the LMT.

Abstract

We report on the results of the on-sky test and science demonstration conducted with the 2 mm receiver system, B4R, on the 50 m Large Millimeter Telescope (LMT), located at an altitude of 4600 m in Mexico. The B4R receiver was developed based on the dual-polarization sideband-separating mixer technology of the Atacama Large Millimeter/submillimeter Array, and is equipped with a fast Fourier transform digital spectrometer, XFFTS. The primary science objective is the spectroscopic redshift identification of high-redshift dusty star-forming galaxies, complementing the existing 3 mm Redshift Search Receiver by enabling the detection of multiple carbon monoxide lines. Additionally, the B4R receiver broadens the range of science cases possible with the LMT, including astrochemistry, as the 2 mm band encompasses unique molecular lines such as deuterated molecules and shock tracers. During on-site commissioning in 2018 and 2019, we successfully demonstrated on-the-fly mapping and position-switching observations toward the Orion Molecular Cloud 1 and bright high-redshift dusty star-forming galaxies, respectively. We confirmed that the installed B4R system largely met its basic performance specifications. Furthermore, we measured the LMT's aperture efficiencies across the entire B4R frequency range (130-160 GHz), finding them to be roughly consistent with expectations based on a surface accuracy of 100 $\mu$m and the receiver optics design. These results with the B4R will enable the most sensitive single-dish spectroscopic observations at 2 mm using the LMT.