Rings and gaps in the disc around Elias 24 revealed by ALMA

G Dipierro,A Sargent,G Laibe,M Tazzari,S Andrews,J A Greaves,G Lodato,C Hall,H Linz,R D Alexander,W Kwon,C J Chandler,L Mundy,T Henning,J M Carpenter,D Wilner,L Testi,L Ricci,L Pérez

doi:10.1093/mnras/sty181

Abstract

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle 2 observations of the 1.3 mm dust continuum emission of the protoplanetary disc surrounding the T Tauri star Elias 24 with an angular resolution of $\sim 0.2"$ ($\sim 28$ au). The dust continuum emission map reveals a dark ring at a radial distance of $0.47"$ ($\sim 65$ au) from the central star, surrounded by a bright ring at $0.58"$ ($\sim 81$ au). In the outer disc, the radial intensity profile shows two inflection points at $0.71"$ and $0.87"$ ($\sim 99$ and $121$ au respectively). We perform global three-dimensional smoothed particle hydrodynamic gas/dust simulations of discs hosting a migrating and accreting planet. Combining the dust density maps of small and large grains with three dimensional radiative transfer calculations, we produce synthetic ALMA observations of a variety of disc models in order to reproduce the gap- and ring-like features observed in Elias 24. We find that the dust emission across the disc is consistent with the presence of an embedded planet with a mass of $\sim 0.7\, \mathrm{M_{\mathrm{J}}}$ at an orbital radius of $\sim$ 60 au. Our model suggests that the two inflection points in the radial intensity profile are due to the inward radial motion of large dust grains from the outer disc. The surface brightness map of our disc model provides a reasonable match to the gap- and ring-like structures observed in Elias 24, with an average discrepancy of $\sim$ 5% of the observed fluxes around the gap region.

Highlights

With the advent of the new generation of radio interferometers and improvements in near-infrared imaging, the field of protoplanetary discs is currently being revolutionized
We have carried out a large number of disc+planet gas/dust simulations in order to determine the disc models that provide a satisfactory match with the radial intensity profile of the dust continuum emission as observed by Atacama Large Millimeter/sub-millimeter Array (ALMA)
If we assume that the shallow gap observed by ALMA corresponds to a shallow gap in the dust density distribution created by a low mass planet, we can reasonably expect that the planet is still largely embedded in the protoplanetary disc, migrating and accreting mass due to the large gas density around its location

Summary

Introduction

With the advent of the new generation of radio interferometers and improvements in near-infrared imaging, the field of protoplanetary discs is currently being revolutionized. Dust rings have been detected in a number of young and evolved protoplanetary discs by high-fidelity and high-resolution observations both in scattered light emission (de Boer et al 2016; Ginski et al 2016; van Boekel et al 2017; Pohl et al 2017) and dust thermal emission (ALMA Partnership et al 2015; Canovas et al 2016; Andrews et al 2016; Isella et al 2016; Perez et al 2016; van der Plas et al 2017; Loomis et al 2017; Fedele et al 2017a,b; Hendler et al 2017) The origin of these structures and their link to the planet formation process is still debated. By analyzing optically thin continuum observations of HL Tau at 7 mm, Carrasco-Gonzalez et al (2016) suggested that the high dust densities measured in the inner rings of HL Tau might be a sign of the formation of gravitationally bound fragments in the rings

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