Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VI. Discovery of a class I methanol maser transition and its association with acetaldehyde
Year: 2026
Type: preprint
Abstract: CH3OH masers that are collisionally pumped, referred to as `class I', commonly trace shock interfaces in star-forming regions, but their incidence in low-mass protostars remains poorly quantified. We use data from the COMPASS ALMA Large Program to establish the occurrence, spatial origin, and excitation of a newly detected class I CH3OH maser at 302.9 GHz towards low-mass protostars and to test whether its pumping environments exhibit signatures of shock-driven complex chemistry. COMPASS provides unbiased line surveys of 11 sources between 279.0 and 311.7 GHz at typical angular resolutions of 0.3"-0.5". Rotation diagram analysis of departures from LTE in the 302.9 GHz CH3OH excitation robustly reveals masing in seven of 11 sources, with peak brightness temperatures from a few to ~10^3 K. The brightest detection is towards HOPS 108 and is likely associated with the powerful outflow from the nearby intermediate-mass protostar HOPS 370. Excluding this case, the maser is detected in six of ten low-mass protostars (60%). All six are Class 0 sources interacting with dense ambient material, whereas the non-detections comprise three Class I sources and one isolated Class 0 core, indicating a preference for early evolutionary stages and gas-rich environments for outflow-ambient medium interactions. The maser emission is spatially coincident with thermal CH3OH along outflow cavity walls and bow shocks, but is more compact and knot-like. Among the surveyed COMs, only CH3CHO closely traces the shocked morphology of the 302.9 GHz maser, and only around HOPS 108. These results show that class I CH3OH masers in low-mass protostellar systems are more prevalent than previously recognised and preferentially occur in younger, more embedded sources. More sensitive CH3CHO observations are needed to test whether a similar relationship with shock-driven chemistry also applies in the low-mass regime.
Source: arXiv (Cornell University)
Authors: Jeong, Jae-Hong, Lee, Jeong-Eun, Jørgensen, Jes K., Coutens, Audrey, Drozdovskaya, Maria N., Plunkett, Adele L., Belloche, Arnaud, Maret, Sébastien, Yun, Hyeong-Sik, de Miera, Fernando Cruz-Sáenz, Harsono, Daniel, Hoff, Merel L. R. van 't, Kim, Chul-Hwan, Kóspál, Ágnes, McGuire, Brett A., Nazari, Pooneh, Spezzano, Silvia, Yang, Yao-Lun, Zeng, Shaoshan
Institutions: Seoul National University, University of Copenhagen, Institut de Recherche en Astrophysique et Planétologie, University of Bern, Physikalisch-Meteorologisches Observatorium Davos, National Radio Astronomy Observatory, Max Planck Institute for Radio Astronomy, Institut de Planétologie et d'Astrophysique de Grenoble, National Tsing Hua University, Tsinghua University, Purdue University West Lafayette, Konkoly Observatory, Max Planck Institute for Astronomy, Massachusetts Institute of Technology, European Southern Observatory, European Southern Observatory, Max Planck Institute for Extraterrestrial Physics, RIKEN
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Gruber Foundation, National Radio Astronomy Observatory, European Commission, Centre National d’Etudes Spatiales, Korea Astronomy and Space Science Institute, National Research Foundation of Korea, Max-Planck-Gesellschaft, Centre National de la Recherche Scientifique, National Astronomical Observatory of Japan, Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, Ministry of Science and ICT, South Korea, National Science and Technology Council, Jess and Mildred Fisher College of Science and Mathematics, RIKEN, National Institutes of Natural Sciences, Nemzeti Kutatási, Fejlesztési és Innovaciós Alap
OpenAlex ID: W7171504447