Hernández-Cruz, Luis Andrés, Zamora-Avilés, Manuel, Luna, Abraham, Naranjo-Romero, Raúl, Franco, José, Palau, Aina, García-Pérez, Alejandro, Ballesteros-Paredes, Javier and Becerril-Tapia, Marcial  ORCID: https://orcid.org/0000-0002-8739-1731
2026.
Synthetic polarization observations of magnetized pillars in H ii regions: Assessing the reliability of the Davis–Chandrasekhar–Fermi method.
Monthly Notices of the Royal Astronomical Society
551
(3)
, stag1499.
10.1093/mnras/stag1499
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Abstract
We investigated the morphology and strength of magnetic fields in pillar-shaped structures at the boundaries of H ii regions by combining three-dimensional radiation-magnetohydrodynamic (R-MHD) simulations with synthetic polarimetric and molecular-line observations. Our analysis focuses on a self-consistently formed pillar as a proof of concept to test the Davis-Chandrasekhar-Fermi (DCF) method under externally driven conditions. The pillar arises as an ionization front compresses a dense clump, producing a magnetically aligned, elongated structure whose morphology and field configuration resemble systems such as the pillars in M16. Synthetic 850 μm dust-polarization maps reproduce the pillar’s large-scale magnetic-field morphology, confirming polarimetry as a reliable tracer of magnetic-field geometry. To evaluate DCF-based methods, we extract local density and velocity dispersion self-consistently from synthetic 13CO observations and measure polarization-angle dispersion using single-Gaussian fits to the synthetic polarization-angle distributions. We find that DCF-based methods systematically overestimate the intrinsic plane-of-sky magnetic-field strength by average factors of ~7 for the classical DCF method and ~5 for the modified Skalidis & Tassis formulation. This overestimation is already present in the full-pillar measurement and is not removed by applying polarimetric S/N cuts or by excluding the dynamically complex head. We attribute the discrepancy to external compression by the expanding H ii region, which organizes the magnetic field on pillar scales while driving non-thermal gas motions. Consequently, the measured velocity and polarization-angle dispersions no longer trace the same turbulence-driven perturbation field assumed by DCF. Our results highlight the need for caution when applying DCF-based analyses to pillars or other externally compressed structures.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Schools > Physical, Chemical & Environmental Sciences |
| Publisher: | Oxford University Press |
| ISSN: | 0035-8711 |
| Date of First Compliant Deposit: | 13 August 2026 |
| Last Modified: | 08 Oct 2026 10:45 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/188979 |
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