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

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.

arXiv comment6 pages, 4 figures, accepted for publication in MNRAS Letters

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• Substructures in Compact Disks of the Taurus Star-forming Region
• The surprising evolution of the shadow on the TW Hya disk
• The time evolution of $M_{\mathrm{d}}/\dot{M}$ in protoplanetary discs as a way to disentangle between viscosity and MHD winds
• Testing velocity kinks as a planet-detection method: Do velocity kinks in surface gas emission trace planetary spiral wakes in the midplane continuum?
• From traffic jams to roadblocks: The outer regions of TW Hya with ALMA Band 8