Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas
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 (αvir). Using a JCMT-SCUBA2 850 micron 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 αvir, indicating that they are predominantly gravitationally unbound at the approximately 86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and αvir for the full cloud sample, the upper quantiles of the SFE distribution show progressively stronger negative trends with increasing αvir. 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-αvir CO-bright clouds in the observed sample. The substantial scatter in the SFE-αvir 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 αvir and instantaneous SFE difficult to recover for individual GMCs.
Related
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BibTeX
@misc{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},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18408},
eprint = {2609.18408},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18408},
note = {CC BY 4.0},
}
RIS
TY - UNPB
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 - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.18408
UR - https://arxiv.org/abs/2609.18408
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 JCMT-SCUBA2 850 micron 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 approximately 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.
ER -