The ALMA survey to Resolve exoKuiper belt Substructures (ARKS)

V. Comparison between scattered light and thermal emission

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
³ Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴ Academia Sinica Institute of Astronomy and Astrophysics, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sect. 4, Roosevelt Rd, Taipei 106319, Taiwan
⁵ Aix Marseille Université, CNRS, CNES, LAM, Marseille, France
⁶ Department of Astronomy and Steward Observatory, The University of Arizona, 933 North Cherry Ave, Tucson, AZ 85721, USA
⁷ Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁸ Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Dr., Middletown, CT 06459, USA
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, 38200 Tenerife, Spain
¹² Joint ALMA Observatory, Avenida Alonso de Córdova 3107, Vitacura 7630355, Santiago, Chile
¹³ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁴ Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720-3411, USA
¹⁵ Large Binocular Telescope Observatory, The University of Arizona, 933 North Cherry Ave, Tucson, AZ 85721, USA
¹⁶ Astronomy Department, University of California, Berkeley, CA 94720, USA
¹⁷ SETI Institute, Carl Sagan Center, 339 Bernardo Ave., Suite 200, Mountain View, CA 94043, USA
¹⁸ Max-Planck Institute für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁹ Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
²⁰ Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergässchen 2–3, 07745 Jena, Germany
²¹ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
²² Department of Physics and Astronomy, Johns Hopkins University, 3400 N Charles Street, Baltimore, MD 21218, USA
²³ Herzberg Astronomy & Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E9, Canada
²⁴ Department of Physics & Astronomy, University of Victoria, 3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada
²⁵ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, MTA Centre of Excellence, Konkoly-Thege Miklós út 15–17, 1121 Budapest, Hungary
²⁶ Institut für Astrophysik (IfA), University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
²⁷ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
²⁸ Departamento de Física, Universidad de Santiago de Chile, Av. Víctor Jara 3493, Santiago, Chile
²⁹ Millennium Nucleus on Young Exoplanets and their Moons (YEMS), Chile
³⁰ Center for Interdisciplinary Research in Astrophysics Space Exploration (CIRAS), Universidad de Santiago, Chile
³¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

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Received: 21 July 2025
Accepted: 3 December 2025

Abstract

Context. Debris discs are analogues to our own Kuiper belt around main-sequence stars and are therefore referred to as exoKuiper belts. They have been resolved at high angular resolution at wavelengths spanning the optical/near-infrared to the submillimetre-millimetre regime. Short wavelengths can probe the light scattered by such discs, which is dominated by micron-sized dust particles, while millimetre wavelengths can probe the thermal emission of millimetre-sized particles. Determining differences in the dust distribution between millimetre- and micron-sized dust is fundamental to revealing the dynamical processes affecting the dust in debris discs.

Aims. We aim to compare the scattered light from the discs of the ‘ALMA survey to Resolve exoKuiper belt Substructures’ (ARKS) with the thermal emission probed by ALMA. We focus on the radial distribution of the dust, and we also put constraints on the presence of giant planets in those systems.

Methods. We used high-contrast scattered light observations obtained with VLT/SPHERE, GPI, and the HST to uniformly study the dust distribution in those systems and compare it to the dust distribution extracted from the ALMA observations carried out in the course of the ARKS project. We also set constraints on the presence of planets by using these high-contrast images combined with exoplanet evolutionary models.

Results. Fifteen of the 24 discs comprising the ARKS sample are detected in scattered light, with TYC 9340-437-1 being imaged for the first time at near-infrared wavelengths. For six of those 15 discs, the dust surface density seen in scattered light peaks farther out compared to that observed with ALMA. These six discs except one are known to also host cold CO gas. Conversely, the systems without significant offsets are not known to host gas, except one. Moreover, with our scattered light near-infrared images, we achieve typical sensitivities to planets from 1 to 10 M_Jup beyond 10 to 20 au, depending on the system age and distance.

Conclusions. This observational study suggests that the presence of gas in debris discs may affect the small and large grains differently, pushing the small dust to greater distances where the gas is less abundant.