From thermal to magnetic driving: Spectral diagnostics of simulation-based magneto-thermal disc wind models

¹ University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
² Excellence Cluster ORIGINS, Boltzmannstr. 2, 85748 Garching, Germany
³ Astronomy Unit, Department of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482, Potsdam, Germany
⁵ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Golm, Germany
⁶ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

^★ Corresponding author: mweber@usm.lmu.de

Received: 20 September 2025
Accepted: 31 October 2025

Abstract

Context. Disc winds driven by thermal and magnetic processes are thought to play a critical role in protoplanetary disc evolution. However, the relative contribution of each mechanism remains uncertain, particularly in light of their observational signatures.

Aims. We investigate whether spatially resolved emission and synthetic spectral line profiles can be used to distinguish between thermally and magnetically driven winds in protoplanetary discs.

Methods. We modelled three disc wind scenarios with different levels of magnetisation: a relatively strongly magnetised wind (β4), a rather weakly magnetised wind (β6), and a purely photoevaporative wind (PE). Using radiative transfer post-processing, we generated synthetic emission maps and line profiles for [OI] 6300 Å, [NeII] 12.81 μm, and o-H₂ 2.12 μm, and compared them with observational trends in the literature.

Results. We find that the β4 model generally produces broader and more blueshifted low-velocity components across all tracers, consistent with compact emission regions and steep velocity gradients. The β6 and PE models yield narrower profiles with smaller blueshifts, in better agreement with most observed narrow low-velocity components (NLVCs). We also find that some line profile diagnostics, such as the inclination at maximum centroid velocity, are not robust discriminants. However, the overall blueshift and full width at half maximum of the low-velocity components provide reliable constraints. The β4 model reproduces the most extreme blueshifted NLVCs in observations, while most observed winds are more consistent with the β6 and PE models.

Conclusions. Our findings reinforce previous conclusions that most observed NLVCs are compatible with weakly magnetised or purely photo-evaporative flows. The combination of line kinematics and emission morphology offers meaningful constraints on wind-driving physics, and synthetic line modelling remains a powerful tool for probing disc wind mechanisms.