Tracing the large-scale magnetic field morphology in protoplanetary disks using molecular line polarization
In one sentence
A 3-D radiative-transfer survey of which molecular lines are best suited to mapping the large-scale magnetic-field geometry in protoplanetary disks — and the answer turns out to be high-dipole-moment species like HCN, especially where the gas is densest.
What’s the question?
Polarized line emission carries the information you need to reconstruct the magnetic-field morphology of a protoplanetary disk — but only some lines, in some regions, will polarize strongly enough to be useful. Which combinations of molecule and tracer geometry give you a clean shot at the field?
What did we do?
Using PORTAL, I ran 3-D polarized radiative-transfer models of a fiducial disk over a grid of molecular tracers (CO, HCN, CN, and others) and physical conditions, mapping where each species polarizes meaningfully. The headline result: molecules with strong dipole moments and modest collisional rate coefficients — HCN being the prime example — polarize across most of the disk and reach the highest signal levels in the dense inner regions where magnetic fields matter most for accretion. CO, by contrast, only polarizes meaningfully in the cold outer disk.
Why does it matter?
The paper is essentially an observer’s guide for the next generation of disk magnetic-field campaigns: pick HCN if you want the inner disk, pick CN for the strong-field directional information from broadening (see Lankhaar & Teague 2023), pick CO for the outermost regions.
My role
First author. Ran the radiative-transfer models, did the analysis, and wrote the paper.