[Paper Review] A super-resolution analysis of the DSHARP survey: Substructure is common in the inner 30 au

Jeff Jennings, Richard A Booth+3 more|arXiv (Cornell University)|Mar 3, 2021

Astrophysics and Star Formation StudiesPhysics and Astronomy41 references39 citations

TL;DR

This study applies the super-resolution 1D visibility-fitting code frank to all 20 DSHARP protoplanetary disc sources, revealing that substructure—especially in the inner 30 au—is significantly more common and detailed than previously seen in CLEAN images. The method achieves a mean factor of 4.3 higher baseline resolution than CLEAN images, uncovering deeper, wider gaps and narrower, brighter rings, demonstrating that the apparent scarcity of inner disc substructure in DSHARP is an artifact of CLEAN's resolution limits, not intrinsic rarity.

ABSTRACT

The DSHARP survey evidenced the ubiquity of substructure in the mm dust distribution of large, bright protoplanetary discs. Intriguingly, these datasets have yet higher resolution information that is not recovered in a CLEAN image. We first show that the intrinsic performance of the CLEAN algorithm is resolution-limited. Then analyzing all 20 DSHARP sources using the 1D, super-resolution code Frankenstein (frank), we accurately fit the 1D visibilities to a mean factor of 4.3 longer baseline than the Fourier transform of the CLEAN images and a factor of 3.0 longer baseline than the transform of the CLEAN component models. This yields a higher resolution brightness profile for each source, identifying new substructure interior to 30 au in multiple discs; resolving known gaps to be deeper, wider, and more structured; and known rings to be narrower and brighter. Across the survey, high contrast gaps are an average 14% wider and 44% deeper in the frank profiles relative to CLEAN, and high contrast rings are an average 26% narrower. Categorizing the frank brightness profiles into trends, we find that the relative scarcity of features interior to 30 au in the survey's CLEAN images is an artifact of resolving power, rather than an intrinsic rarity of inner disc (or compact disc) substructure. Finally the rings in the frank profiles are narrower than the previously inferred deconvolved widths, indicating smaller alpha / St ratios in the local gas disc.

Motivation & Objective

• To investigate whether the apparent scarcity of substructure in the inner 30 au of DSHARP discs is due to resolution limits of the CLEAN algorithm.
• To test if super-resolution visibility fitting can recover higher-resolution brightness profiles from existing ALMA data.
• To quantify the extent and nature of substructure in the inner discs of the DSHARP sample beyond what CLEAN imaging reveals.
• To assess the implications of super-resolved profiles for dust evolution and planet-disk interaction models, particularly regarding gap and ring morphology.

Proposed method

• The 1D super-resolution code frank is used to nonparametrically fit the azimuthally averaged visibility data of each DSHARP source.
• Frank reconstructs the brightness profile via a Fourier-Bessel series fit to the real component of deprojected, unbinned visibilities.
• The method performs a discrete Hankel transform (DHT) to link the visibility domain to the radial brightness profile in real space.
• The technique avoids the resolution degradation inherent in CLEAN by not convolving with a CLEAN beam, enabling higher effective resolution.
• The method is applied to all 20 DSHARP sources, with results compared to both CLEAN images and CLEAN component models.
• Hyperparameters are tuned efficiently, with all fits completed in under one minute per source using open-source code.

Experimental results

Research questions

• RQ1 To what extent is the lack of observed substructure in the inner 30 au of DSHARP discs an artifact of CLEAN's resolution limitations rather than intrinsic disc properties?
• RQ2 How much higher resolution can be achieved in brightness profile reconstruction using super-resolution visibility fitting compared to CLEAN imaging?
• RQ3 What new substructure features—such as deeper gaps, narrower rings, or inner disc structure—emerge in the super-resolved profiles?
• RQ4 How do the super-resolved ring widths constrain the local gas disc's α/St ratio, and do they require lower values than previously inferred?
• RQ5 What geometric viewing effects related to inner disc vertical structure are revealed by the super-resolved profiles?

Key findings

• The frank super-resolution analysis achieves a mean factor of 4.3 higher baseline resolution than the CLEAN image Fourier transform and 3.0 higher than the CLEAN component model transform.
• High-contrast gaps in the frank profiles are, on average, 14% wider and 44% deeper than in CLEAN images, while high-contrast rings are 26% narrower.
• Substructure in the inner 30 au is significantly more common than indicated by CLEAN images, indicating that the apparent scarcity is an artifact of resolution.
• The frank brightness profiles reveal new substructure interior to 30 au in multiple discs, including deeper, wider, and more structured gaps and narrower, brighter rings.
• The super-resolved ring widths imply that lower α/St ratios than previously inferred are required to explain the data, suggesting smaller turbulent viscosity in the local gas disc.
• A geometric viewing effect related to inner disc vertical structure is identified in 10 of the 20 DSHARP sources, indicating that inclination and flaring influence observed brightness profiles.