Oral Presentation
A Polarization-Based Framework for Constraining Dust Mass in Optically Thick Class 0/I Disks
Presenter: Naoya Kitade (National Astronomical Observatory of Japan)
When does planet formation begin? Addressing this question requires measuring dust masses in Class 0/I disks, but their high optical depth at millimeter wavelengths means that continuum observations alone yield only lower limits.
In this work, we present a new polarization-based framework to measure the dust mass in such optically thick disks. The key obstacle is that continuum emission cannot disentangle the dust optical depth τ from the albedo ω. Scattering polarization breaks this degeneracy because its dependence on τ and ω differs fundamentally from that of continuum emission. By solving the radiative transfer equation for a plane-parallel slab, we quantify the τ- and ω-dependences of scattering polarization and derive a fitting formula for the polarization directly applicable to ALMA polarization data. Applying this formula to polarization data and combining the result with continuum observations, we reliably constrain the optical depth up to τ ~ 5, enabling direct dust mass measurements that have been inaccessible to continuum-only analyses. This new framework for measuring dust masses opens a path to testing whether planet formation is already underway in the embedded phase, directly linking the youngest disks to the more evolved Class II stage.
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