No Significant Correlation between Line-emission and Continuum Substructures in the Molecules with ALMA at Planet-forming Scales Program

TL;DR

This study finds no universal correlation between line emission substructures and dust continuum features in planet-forming disks, challenging previous assumptions about their causal relationship, with some notable exceptions.

Contribution

It rigorously tests the correlation between line emission and dust structures using statistical analysis, revealing the lack of a universal link and identifying specific outliers.

Findings

No statistically significant universal correlation found.

Chemical rings in MWC 480 strongly correlated with dust gaps.

Gaps in CO isotopologues moderately correlated with dust rings.

Abstract

Recently, the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program reported a high number of line emission substructures coincident with dust rings and gaps in the continuum emission, suggesting a causal link between these axisymmetric line emission and dust continuum substructures. To test the robustness of the claimed correlation, we compare the observed spatial overlap fraction in substructures with that from the null hypothesis, in which the overlap is assumed to arise from the random placement of line emission substructures. Our results reveal that there is no statistically significant evidence for a universal correlation between line emission and continuum substructures, questioning the frequently-made link between continuum rings and pressure bumps. The analysis also clearly identifies outliers. The chemical rings and the dust gaps in MWC 480 appear to be strongly correlated (${>}4\sigma$), and the gaps in the CO isotopologues tend to moderately (${\sim}3\sigma$) correlate with dust rings.