2025PASJ...77.1224Y

We present the results of mapping and single-point spectral scans toward Orion-KL/OMC-1 performed as science demonstrations of a 2 mm superconductor-insulator-superconductor receiver, named the Band 4 Receiver (B4R), installed on the Large Millimeter Telescope (LMT), with a diameter of 50 m. To prove the capabilities of mapping and spectral scans with the B4R on the LMT, commissioning observations were conducted employing the on-the-fly mapping technique toward Orion-KL/OMC-1, which covers a map size of $5{^{\prime}} \times 5{^{\prime}}$. These mapping observations were performed with two frequency settings providing 10 GHz in total (131.4-133.9 and 145.1-147.6 GHz; 136.2-138.7 and 149.9-152.4 GHz) with a frequency resolution of 76.293 kHz. In this study, we conducted spectral line identification analysis for the hot core and compact ridge regions in the Orion-KL with a beam size of $11{^{\prime \prime }}$-$12{^{\prime \prime }}$. We detected nearly 400 emission lines and identified two recombination lines and 29 molecular species, including isotopologues, deuterated molecules, and vibrational excited states, despite the short integration time. These results of line detection are consistent with those of previous studies. The 29 molecular species include nitrogen (N)-bearing complex organic molecules (COMs) and oxygen (O)-bearing COMs. To demonstrate the capability of the B4R in astrochemistry, we conducted detailed analyses of column densities, rotational temperatures, and relative abundances with respect to H$_2$ on two representative COMs, N-bearing C$_2$H$_5$CN and O-bearing CH$_3$OCHO in the central $40{^{\prime \prime }} \times 40{^{\prime \prime }}$ area of the map. The wide bandwidth of 10 GHz enabled the use of 8 and 34 emission lines, respectively. The spatial differences in the physical and chemical properties between the above two molecules were derived at a spatial resolution of ${\sim}12{^{\prime \prime }}$. The B4R on the LMT was successfully demonstrated to be powerful for mapping and spectral scans and to have high potential for the study of interstellar chemistry.