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Dust properties in the 13 au gap of HL Tau unresolved due to modeling failure

Determine the dust surface density and maximum grain size within the 13 au gap of the HL Tau protoplanetary disk by achieving higher angular resolution at long wavelengths and refining radiative transfer modeling, since the current multi-wavelength 1D slab model constrained by ALMA and VLA continuum data fails to reproduce the observed emission at these radii.

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Background

The authors fit radial spectral energy distributions using a 1D slab model across five wavelengths (0.45, 0.87, 1.3, 2.1, and 7.0 mm), considering both compact and porous grains. At the 13 au gap, the model yields an unphysical jump in grain size and cannot match the observed emission, which the authors attribute to limited angular resolution and strong depletion of large grains in the gap.

They conclude that higher angular resolution observations at long wavelengths (e.g., with the ngVLA) are necessary to constrain the dust properties at these radii, highlighting an unresolved characterization of the gap’s dust content.

References

Our models find a sudden, and likely unphysical, increase in particle size at the 13 au gap. However, figures \ref{Fig:A1} and \ref{Fig:A2} show that our models are in fact incapable of reproducing the observed emission at these radii.

— Into the thick of it: ALMA 0.45 mm observations of HL Tau at 2 au resolution (2404.04164 - Guerra-Alvarado et al., 5 Apr 2024) in Section 4.1 (Discussion: Modeling of the dust properties)