Dust Traps and the Formation of Cavities in Transition Discs: A millimetre to sub-millimetre comparison survey

TL;DR

This study compares millimetre and sub-millimetre observations of transition discs to understand dust cavity formation, suggesting dust traps caused by companions as a key mechanism.

Contribution

It provides the first direct comparison of dust emission at 8.8 mm and sub-mm wavelengths in transition discs, revealing consistent cavity sizes across wavelengths.

Findings

Cavities at 8.8 mm and sub-mm wavelengths peak at the same radius.

Dust traps likely caused by companions are inferred from similar cavity sizes.

Resolved cavities in 8 of 14 discs support the dust trapping hypothesis.

Abstract

The origin of the inner dust cavities observed in transition discs remains unknown. The segregation of dust and size of the cavity is expected to vary depending on which clearing mechanism dominates grain evolution. We present the results from the Discs Down Under program, an 8.8 mm continuum Australia Telescope Compact Array (ATCA) survey targeting 15 transition discs with large (> 20 au) cavities, and compare the resulting dust emission to Atacama Large millimetre/sub-millimetre Array (ALMA) observations. Our ATCA observations resolve the inner cavity for 8 of the 14 detected discs. We fit the visibilities and reconstruct 1D radial brightness models for 10 sources with a S/N > 5sigma. We find that, for sources with a resolved cavity in both wavebands, the 8.8 mm and sub-mm brightness distributions peak at the same radius from the star. We suggest that a similar cavity size for 8.8 mm and sub-mm dust grains is due to a dust trap induced by the presence of a companion.