Metal-poor molecular clouds in dwarf galaxies at parsec-scale resolution
Abstract
Understanding how stars form at low metallicity is challenging because carbon monoxide (CO) emission, which usually probes the molecular gas reservoir, is faint, and tends to be concentrated in parsec-scale clumps. To overcome this difficulty, in order to study the molecular clouds in metal-poor environments, we have acquired CO(2-1) ALMA maps at 3-4 pc resolution of four nearby dwarf galaxies with nebular (O/H) metallicities ranging from roughly 1/9 Z_sun to 1/3 Z_sun. Significant CO signal in the cubes has been identified through two masks, a ``strict'', high-confidence, mask and a ``broad'' one for better completeness. The former traces the cores of the clouds, while the latter includes fainter emission in the vicinity of the cores. Through a cloud-finding algorithm applied to the two sets of masked cubes, we have identified more than 200 molecular clouds across the sample, with roughly 50 in NGC3109, at 1/9 Z_sun, the lowest metallicity parsec-scale cloud population yet observed. The best-fit size-linewidth relations for the resolved clouds are similar among all galaxies, with a slope like the Milky Way (MW), but with lower velocity dispersion at a given cloud size. For a fixed CO-to-H_2 MW conversion factor, the cloud virial ratios tend to be large, and show a weak increasing trend with increasing cloud size, and decreasing apparent surface densities and metallicity. We find evidence for faint but significant CO emission outside CO-bright cores, spanning similar velocities to those observed in the cores. We attribute this to effective shielding by gas and dust, despite the low metallicities of our sample, since the CO tends to be cospatial with dust as traced by far-infrared emission.
Related
- Molecular atlas of nearby galaxies through sensitive high-resolution multi-band molecular line surveys
- Warm Molecular Hydrogen in Metal-poor Compact Galaxies: A Uniform JWST/MIRI Archival Analysis
- NOEMA Observations of the Center of M33: A Parsec-scale Molecular Filament and an Ordered Gas-Star-Formation Sequence
- A High Resolution View of Three Massive Young Stellar Objects in the Magellanic Clouds
- Carbon addition as the dominant pathway for aromatic growth in dense molecular clouds
BibTeX
@misc{hunt2026metalpoor,
title = {{Metal-poor molecular clouds in dwarf galaxies at parsec-scale resolution}},
author = {L. K. Hunt and M. Heyer and U. Lisenfeld and A. Weiss and A. Bolatto and E. Brinks and M. Rubio and D. Calzetti and F. Combes and E. Corbelli and B. G. Elmegreen and S. Garcia-Burillo and C. Henkel and K. M. Menten and L. J. Smith and A. Adamo and B. T. Draine and D. A. Hunter and N. Izumi and K. E. Johnson},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27064},
eprint = {2610.27064},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27064},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Metal-poor molecular clouds in dwarf galaxies at parsec-scale resolution
AU - L. K. Hunt
AU - M. Heyer
AU - U. Lisenfeld
AU - A. Weiss
AU - A. Bolatto
AU - E. Brinks
AU - M. Rubio
AU - D. Calzetti
AU - F. Combes
AU - E. Corbelli
AU - B. G. Elmegreen
AU - S. Garcia-Burillo
AU - C. Henkel
AU - K. M. Menten
AU - L. J. Smith
AU - A. Adamo
AU - B. T. Draine
AU - D. A. Hunter
AU - N. Izumi
AU - K. E. Johnson
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.27064
UR - https://arxiv.org/abs/2610.27064
AB - Understanding how stars form at low metallicity is challenging because carbon monoxide (CO) emission, which usually probes the molecular gas reservoir, is faint, and tends to be concentrated in parsec-scale clumps. To overcome this difficulty, in order to study the molecular clouds in metal-poor environments, we have acquired CO(2-1) ALMA maps at 3-4 pc resolution of four nearby dwarf galaxies with nebular (O/H) metallicities ranging from roughly 1/9 Z_sun to 1/3 Z_sun. Significant CO signal in the cubes has been identified through two masks, a ``strict'', high-confidence, mask and a ``broad'' one for better completeness. The former traces the cores of the clouds, while the latter includes fainter emission in the vicinity of the cores. Through a cloud-finding algorithm applied to the two sets of masked cubes, we have identified more than 200 molecular clouds across the sample, with roughly 50 in NGC3109, at 1/9 Z_sun, the lowest metallicity parsec-scale cloud population yet observed. The best-fit size-linewidth relations for the resolved clouds are similar among all galaxies, with a slope like the Milky Way (MW), but with lower velocity dispersion at a given cloud size. For a fixed CO-to-H_2 MW conversion factor, the cloud virial ratios tend to be large, and show a weak increasing trend with increasing cloud size, and decreasing apparent surface densities and metallicity. We find evidence for faint but significant CO emission outside CO-bright cores, spanning similar velocities to those observed in the cores. We attribute this to effective shielding by gas and dust, despite the low metallicities of our sample, since the CO tends to be cospatial with dust as traced by far-infrared emission.
ER -