Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas
13 affiliations
- 1University of Chinese Academy of Sciences
- 2Chinese Academy of Sciences
- 3Max Planck Institute for Astronomy
- 4Department of Physics
- 5National Taiwan Normal University
- 6New Cornerstone Science Laboratory
- 7Max-Planck-Institut für Extraterrestrische Physik
- 8Beijing Normal University
- 9Guangxi University
- 10Nanjing University
- 11Key Laboratory of Modern Astronomy and Astrophysics
- 12Korea Astronomy and Space Science Institute
- 13National Astronomical Observatory of Japan
Abstract
The Andromeda galaxy (M31) exhibits a systematically low star formation efficiency (SFE) compared to other star-forming galaxies. Star formation is thought to be regulated by the mass of gravitationally bound gas. To investigate whether the low SFE in M31 originates from a scarcity of such bound gas, we analyze the dynamical state of its giant molecular cloud (GMC) population by estimating their virial parameters ( α vir ). Using a James Clerk Maxwell Telescope SCUBA2 850 μ m dust-continuum GMC catalog as the parent sample, we combine it with IRAM 30 m CO(1–0) data to define a working sample of 173 GMCs and derive their kinematic properties. Most analyzed GMCs exhibit high α vir , indicating that they are predominantly gravitationally unbound at the ∼86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and α vir for the full cloud sample, the upper quantiles of the SFE distribution show progressively stronger negative trends with increasing α vir . This upper-tail trend may arise from the combined effects of the virial parameter limiting the upper range of SFE values accessible to the GMC population and feedback-driven disruption reducing the number of high-SFE, high- α vir CO-bright clouds in the observed sample. The substantial scatter in the SFE- α vir plane likely reflects the diverse evolutionary stages of GMCs, the temporal mismatch between gas and star formation tracers, and the limitations of a cloud-averaged virial parameter as a tracer of internal dynamical structure, making a simple one-to-one correspondence between α vir and instantaneous SFE difficult to recover for individual GMCs.
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BibTeX
@article{deng2026star,
title = {{Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas}},
author = {Fangyuan Deng and Sihan Jiao and Hauyu Baobab Liu and Jingwen Wu and Henrik Beuther and Fanyi Meng and Caroline Gieser and Yuxin Lin and Di Li and Chao-Wei Tsai and Junzhi Wang and Zhi-Yu Zhang and Fengwei Xu and Jakob den Brok and Linjing Feng and Zongnan Li and Yuxiang Liu},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea993},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea993},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas
AU - Fangyuan Deng
AU - Sihan Jiao
AU - Hauyu Baobab Liu
AU - Jingwen Wu
AU - Henrik Beuther
AU - Fanyi Meng
AU - Caroline Gieser
AU - Yuxin Lin
AU - Di Li
AU - Chao-Wei Tsai
AU - Junzhi Wang
AU - Zhi-Yu Zhang
AU - Fengwei Xu
AU - Jakob den Brok
AU - Linjing Feng
AU - Zongnan Li
AU - Yuxiang Liu
PY - 2026
DA - 2026/10/13
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea993
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea993
AB - The Andromeda galaxy (M31) exhibits a systematically low star formation efficiency (SFE) compared to other star-forming galaxies. Star formation is thought to be regulated by the mass of gravitationally bound gas. To investigate whether the low SFE in M31 originates from a scarcity of such bound gas, we analyze the dynamical state of its giant molecular cloud (GMC) population by estimating their virial parameters ( α vir ). Using a James Clerk Maxwell Telescope SCUBA2 850 μ m dust-continuum GMC catalog as the parent sample, we combine it with IRAM 30 m CO(1–0) data to define a working sample of 173 GMCs and derive their kinematic properties. Most analyzed GMCs exhibit high α vir , indicating that they are predominantly gravitationally unbound at the ∼86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and α vir for the full cloud sample, the upper quantiles of the SFE distribution show progressively stronger negative trends with increasing α vir . This upper-tail trend may arise from the combined effects of the virial parameter limiting the upper range of SFE values accessible to the GMC population and feedback-driven disruption reducing the number of high-SFE, high- α vir CO-bright clouds in the observed sample. The substantial scatter in the SFE- α vir plane likely reflects the diverse evolutionary stages of GMCs, the temporal mismatch between gas and star formation tracers, and the limitations of a cloud-averaged virial parameter as a tracer of internal dynamical structure, making a simple one-to-one correspondence between α vir and instantaneous SFE difficult to recover for individual GMCs.
SN - 0004-637X
SN - 1538-4357
ER -