Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VI. Discovery of a class I methanol maser transition and its association with acetaldehyde

@misc{jeong2026complex,
  title = {{Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VI. Discovery of a class I methanol maser transition and its association with acetaldehyde}},
  author = {Jae-Hong Jeong and Jeong-Eun Lee and Jes K. Jørgensen and Audrey Coutens and Maria N. Drozdovskaya and Adele L. Plunkett and Arnaud Belloche and Sébastien Maret and Hyeong-Sik Yun and Fernando Cruz-Sáenz de Miera and Daniel Harsono and Merel L. R. van 't Hoff and Chul-Hwan Kim and Ágnes Kóspál and Brett A. McGuire and Pooneh Nazari and Silvia Spezzano and Yao-Lun Yang and Shaoshan Zeng},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.08158},
  eprint = {2610.08158},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.08158},
  note = {CC BY-NC-SA 4.0},
}

TY  - UNPB
TI  - Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VI. Discovery of a class I methanol maser transition and its association with acetaldehyde
AU  - Jae-Hong Jeong
AU  - Jeong-Eun Lee
AU  - Jes K. Jørgensen
AU  - Audrey Coutens
AU  - Maria N. Drozdovskaya
AU  - Adele L. Plunkett
AU  - Arnaud Belloche
AU  - Sébastien Maret
AU  - Hyeong-Sik Yun
AU  - Fernando Cruz-Sáenz de Miera
AU  - Daniel Harsono
AU  - Merel L. R. van 't Hoff
AU  - Chul-Hwan Kim
AU  - Ágnes Kóspál
AU  - Brett A. McGuire
AU  - Pooneh Nazari
AU  - Silvia Spezzano
AU  - Yao-Lun Yang
AU  - Shaoshan Zeng
PY  - 2026
DA  - 2026/10/06
PB  - arXiv
DO  - 10.48550/arxiv.2610.08158
UR  - https://arxiv.org/abs/2610.08158
AB  - 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.
ER  -