B-FROST: B-Fields and star formation across scales with TRAO
Abstract
Context. On average, in our Galaxy, the star formation efficiency (SFE) is of the order of a few percent, which is lower than theoretical predictions. Detailed observational studies of individual molecular clouds may offer insight into the contributing factors to the low galactic SFE. Aims. We investigated the high-latitude molecular cloud MBM12 as part of the B-fields and star formation across scales (B-FROST) survey with the Taeduk Radio Astronomical Observatory (TRAO) to assess why star formation activity in MBM12 is low. Methods. We estimated N(H 2 ) with Herschel dust emission and a dust opacity κ ν derived from near-infrared extinction, 21 cm HI column densities, and far-infrared emission. With 12 CO and 13 CO (J = 1-0) line observations, covering an area of 2.5 • × 3 • at 48 ′′ resolution, we mapped the CO column density N(CO), CO-to-H 2 factor X(CO), and abundance [CO/H 2 ]. We estimated the multi-scale virial parameter α vir and constructed mass-size scaling laws of hierarchical structures with dendrograms. We computed the relative orientation between column density structures and magnetic fields using Planck observations of dust polarisation. Results. We identified four main regions based on velocities with H 2 column densities ranging from 2 × 10 20 -1.3 × 10 22 cm -2 . The CO integrated line intensity, W(CO), increases linearly with N(H 2 ), providing an average X(CO) factor close to the Galactic average. At a low N(H 2 ), X(CO) varies below X Gal due to the fall-off of collisional de-excitation in low-density gas, and above X Gal due to the drop of CO abundances in poorly shielded cloud edges. The hierarchical structures follow a broken power law mass-size relation M = AR α . The values of α vir ranged from 3-60, with the smallest values at 0.1 pc scales. The mass-size relations for the structures with the lowest α vir have scaling factors, A, three times larger than those of high α vir structures, indicating external pressure one order of magnitude larger than the former. We found a transition from parallel to perpendicular relative orientations between column density structures and the magnetic field at N(H 2 ) = 4.5 × 10 21 cm -2 . Conclusions. We provide the first integrated chemical, dynamical, and magnetic field analysis of MBM12. Further investigation into the scale dependence of the mass-size relation and virial parameter can highlight the role of external pressure in regulating the star-formation efficiency.
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BibTeX
@article{vorster2026bfrost,
title = {{B-FROST: B-Fields and star formation across scales with TRAO}},
author = {J M Vorster and J Montillaud and M Juvela and E Falgarone and J Oers and E Mannfors and D Alina and Q Gu and H Kang and C W Lee and S Li and T Liu and K Pattle and V-M Pelkonen and I Ristorcelli and A Zavagno and L V Tóth},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = sep,
doi = {10.1051/0004-6361/202659617},
url = {https://hal.science/hal-05759504v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - B-FROST: B-Fields and star formation across scales with TRAO
AU - J M Vorster
AU - J Montillaud
AU - M Juvela
AU - E Falgarone
AU - J Oers
AU - E Mannfors
AU - D Alina
AU - Q Gu
AU - H Kang
AU - C W Lee
AU - S Li
AU - T Liu
AU - K Pattle
AU - V-M Pelkonen
AU - I Ristorcelli
AU - A Zavagno
AU - L V Tóth
PY - 2026
DA - 2026/09/22
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202659617
UR - https://hal.science/hal-05759504v1
AB - Context. On average, in our Galaxy, the star formation efficiency (SFE) is of the order of a few percent, which is lower than theoretical predictions. Detailed observational studies of individual molecular clouds may offer insight into the contributing factors to the low galactic SFE. Aims. We investigated the high-latitude molecular cloud MBM12 as part of the B-fields and star formation across scales (B-FROST) survey with the Taeduk Radio Astronomical Observatory (TRAO) to assess why star formation activity in MBM12 is low. Methods. We estimated N(H 2 ) with Herschel dust emission and a dust opacity κ ν derived from near-infrared extinction, 21 cm HI column densities, and far-infrared emission. With 12 CO and 13 CO (J = 1-0) line observations, covering an area of 2.5 • × 3 • at 48 ′′ resolution, we mapped the CO column density N(CO), CO-to-H 2 factor X(CO), and abundance [CO/H 2 ]. We estimated the multi-scale virial parameter α vir and constructed mass-size scaling laws of hierarchical structures with dendrograms. We computed the relative orientation between column density structures and magnetic fields using Planck observations of dust polarisation. Results. We identified four main regions based on velocities with H 2 column densities ranging from 2 × 10 20 -1.3 × 10 22 cm -2 . The CO integrated line intensity, W(CO), increases linearly with N(H 2 ), providing an average X(CO) factor close to the Galactic average. At a low N(H 2 ), X(CO) varies below X Gal due to the fall-off of collisional de-excitation in low-density gas, and above X Gal due to the drop of CO abundances in poorly shielded cloud edges. The hierarchical structures follow a broken power law mass-size relation M = AR α . The values of α vir ranged from 3-60, with the smallest values at 0.1 pc scales. The mass-size relations for the structures with the lowest α vir have scaling factors, A, three times larger than those of high α vir structures, indicating external pressure one order of magnitude larger than the former. We found a transition from parallel to perpendicular relative orientations between column density structures and the magnetic field at N(H 2 ) = 4.5 × 10 21 cm -2 . Conclusions. We provide the first integrated chemical, dynamical, and magnetic field analysis of MBM12. Further investigation into the scale dependence of the mass-size relation and virial parameter can highlight the role of external pressure in regulating the star-formation efficiency.
SN - 0004-6361
SN - 1432-0746
ER -