The ALMA survey to Resolve exoKuiper belt Substructures (ARKS)

II. The radial structure of debris discs

¹ Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
² Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Dr., Middletown, CT, 06459, USA
³ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Ave., New York, NY 10010, USA
⁴ Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁵ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
⁶ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁸ Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France
⁹ School of Physics, Trinity College Dublin, the University of Dublin, College Green, Dublin 2, Ireland
¹⁰ Instituto de Astrofísica de Canarias, Vía Láctea S/N, La Laguna, 38200, Tenerife, Spain
¹¹ Departamento de Astrofísica, Universidad de La Laguna, La Laguna, E-38200, Tenerife, Spain
¹² Joint ALMA Observatory, Avenida Alonso de Córdova 3107, Vitacura 7630355, Santiago, Chile
¹³ National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
¹⁴ Department of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
¹⁵ Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720-3411, USA
¹⁶ Department of Astronomy and Steward Observatory, The University of Arizona, 933 North Cherry Ave, Tucson, AZ, 85721, USA
¹⁷ Large Binocular Telescope Observatory, The University of Arizona, 933 North Cherry Ave, Tucson, AZ, 85721, USA
¹⁸ Max-Planck-Insitut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁹ Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
²⁰ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, MTA Centre of Excellence, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
²¹ Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
²² Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergäßchen 2-3, 07745 Jena, Germany
²³ Department of Physics and Astronomy, Johns Hopkins University, 3400 N Charles Street, Baltimore, MD 21218, USA
²⁴ Academia Sinica Institute of Astronomy and Astrophysics, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sect. 4, Roosevelt Rd, Taipei 106319, Taiwan
²⁵ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
²⁶ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
²⁷ Departamento de Física, Universidad de Santiago de Chile, Av. Víctor Jara 3493, Santiago, Chile
²⁸ Millennium Nucleus on Young Exoplanets and their Moons (YEMS), Chile
²⁹ Center for Interdisciplinary Research in Astrophysics Space Exploration (CIRAS), Universidad de Santiago, Chile
³⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

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Received: 16 July 2025
Accepted: 28 October 2025

Abstract

Context. Debris discs are populated by belts of planetesimals, whose structure carries dynamical imprints of planets and the formation and evolutionary history of the planetary system. The relatively faint emission of debris discs has previously made it challenging to obtain a large sample of high-resolution ALMA images to characterise their substructures.

Aims. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) was recently completed to cover the lack of high-resolution observations and to investigate the prevalence of substructures such as radial gaps and rings in a sample of 24 debris discs. This study characterises the radial structure of debris discs in the ARKS programme.

Methods. We modelled all discs with a range of non-parametric and parametric approaches, including those that deconvolve and deproject the image or fit the visibilities directly, in order to identify and quantify the disc substructures.

Results. Across the sample we find that of the 24 discs, 5 host multiple rings, 7 are single rings that display halos or additional low-amplitude rings, and 12 are single rings with at most tentative evidence of additional substructures. The fractional ring widths that we measured are significantly narrower than previously derived values, and they follow a distribution similar to the fractional widths of individual rings resolved in protoplanetary discs. However, there exists a population of rings in debris discs that are significantly wider than those in protoplanetary discs. We also find that discs with steep inner edges consistent with planet sculpting tend to be found at smaller (<100 au) radii, while more radially extended discs tend to have shallower edges more consistent with collisional evolution. An overwhelming majority of discs have radial profiles that are well-described by either a double power law or double-Gaussian parametrisation.

Conclusions. While our findings suggest that it may be possible for some debris discs to inherit their structures directly from pro-toplanetary discs, there exists a sizeable population of broad debris discs that cannot be explained in this way. Assuming that the distribution of millimetre dust reflects the distribution of planetesimals, mechanisms that cause rings in protoplanetary discs to migrate or debris discs to broaden soon after formation may be at play, possibly mediated by planetary migration or scattering.