[P-CG19] Origin and evolution of materials in space

[PCG19-P03] Test observations toward Orion-KL region using 2mm Band 4 Receiver onboard 50m Large Millimeter Telescope

*Teppei Yonetsu¹, Hiroyuki Maezawa¹, Ryohei Kawabe², Yuki Yoshimura³, Bunyo Hatsukade³, Kotaro Kohno³, Tatsuya Takekoshi⁴, Takeshi Sakai⁵, Kunihiko Tanaka⁶, Akio Taniguchi⁷, Yoichi Tamura⁷, Tai Oshima², Yoshito Shimajiri², David Hughes⁸, David Sanchez-Arguelles⁸, Arturo Gomez-Ruiz⁸, Ivan Rodriguez-Montoya⁸, Javier Zaragoza-Cardiel⁸, Edgar Colin⁸, Miguel Chavez-Dagostino⁸, Sergio Rojas⁸, Pete Schloerb⁹, Kamal Souccar⁹, Min Yun⁹ (1.Osaka Prefecture University, 2.NAOJ, 3.University of Tokyo, 4.Kitami Institute of Technology, 5.The University of Electro-Communications, 6.Keio University, 7.Nagoya University, 8.INAOE, 9.UMass)

Keywords:ISM molecules, astrochemistry, star formation, radio lines, telescopes

We carried out test on-the-fly mapping observations toward the high mass star-forming region, Orion-KL located at a distance of about 414 pc from the Sun by using the Band 4 Receiver (B4R) employing 2-mm-band highly sensitive superconducting SIS receivers onboard the 50 m aperture Large Millimeter Telescope (LMT) operated at an altitude of 4600 m in Mexico. B4R allows us to observe both single sidebands for two orthogonal polarizations. The equivalent receive noise temperatures are less than 60 K. Observed areas were 10'x10’ (Oct. 2018) and 5'x5' (Nov. 2019), and the observation frequency bands were 127.9-130.4,131.9-134.4,141.6-144.1,145.6-148.1 GHz and 131.4-133.9,136.2-138.7,145.1-147.6,149.9-152.4 GHz, respectively. The observed area includes the hot molecular core located close to a young protostar as an external heat source. This core is now well-known to contain a variety of complex carbon-chain molecules. On the other hand, the high-density and the comparatively low-temperature region called compact ridge in ~ 7 arcseconds southwest of the hot molecular core has various complex oxygen-bearing organic molecules. The chemical differentiation seen in these dense cores may have been driven by the difference in the physical conditions in their evolutionary/formation processes. Therefore, recently the chemistry in Orion-KL region is well studied by high spatial resolution interferometric observations with ALMA, SMA, etc to understand the formation mechanisms of high-mass stars. In this test observations with 50m-LMT/B4R extensive spread of oxygen-bearing molecules (CH₃OCHO, CH₃OCH₃, etc.) centering on the compact ridge was confirmed. On the other hand, it was found that nitrogen-containing carbon chain molecules (C₂H₅CN, C₂H₃CN, HC₃N, etc.) and sulfur-containing molecules (SO₂, OCS, etc.) widely distributed mainly in the hot core. Systematic changes in the distribution of chemical composition were clearly captured in this region. In addition, the high excitation lines of CH₃OCHO (v₁₈ = 1) and the recombination lines of hydrogen were also detected for the first time in the 2 mm band. In this conference, we will report the results of the analysis of the spatial distributions of the molecular species and the temperature environment obtained toward Orion-KL at a spatial resolution of about 10 arcseconds (~ 0.02 pc) by the 50 m-LMT/B4R.