Unveiling the outer dust disc of TW Hya with deep ALMA observations

TL;DR

Deep ALMA observations of TW Hya reveal a more extensive and structured dust disc than previously known, including new features at 82 au and confirmation of a 52 au excess, highlighting the importance of sensitive, high-resolution imaging.

Contribution

This study demonstrates that combining deep ALMA data with advanced analysis techniques uncovers faint disc structures beyond prior detection limits.

Findings

Disc extends to 100 au, beyond previous estimates

Identification of a new gap at 82 au coinciding with other observations

Confirmation of a 52 au continuum excess

Abstract

The radial extent of millimetre dust in protoplanetary discs is often far smaller than that of their gas, mostly due to processes such as dust growth and radial drift. However, it has been suggested that current millimetre continuum observations of discs do not trace their full extent due to limited sensitivity. In this Letter, we present deep (19 $\mu$Jy beam$^{-1}$) moderate resolution (0.37") ALMA observations at 1 mm of the nearest protoplanetary disc, TW Hya. Using the visibility analysis tool `frank', we reveal a structured millimetre intensity distribution out to 100 au, well beyond previous estimates of 60-70 au. Our analysis suggests the presence of a new millimetre continuum gap at 82 au, coincident with similar features seen in optical/near-infrared scattered light and millimetre molecular line observations. Examination of the fit residuals confirms the presence of the previously reported au-scale continuum excess at 52 au (P.A. = 242.5 degrees). Our results demonstrate the utility of combining deep, moderate resolution observations with super-resolution analysis techniques to probe the faintest regions of protoplanetary discs.