The ALPINE-ALMA [CII] survey: Dust emission effective radius up to 3 kpc in the early Universe

¹ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
e-mail: f.pozzi@unibo.it
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
³ INAF – Osservatorio Astrofisico di Arcetri Firenze, Via Largo Enrico Fermi 5, Firenze, Italy
⁴ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
⁵ Aix-Marseille Univ., CNRS, CNES, LAM, 13388 Marseille, France
⁶ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06000 Nice, France
⁷ INAF – Istituto di Radioastronomia Bologna, Via Gobetti 111, 40129 Bologna, Italy
⁸ Department of Astronomy, Columbia University, New York, NY 10027, USA
⁹ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
¹⁰ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹¹ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
¹² Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
¹³ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla, 4059 Valparaíso, Chile
¹⁴ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
¹⁵ Space Telescope Science Institute, Baltimore, MD 21218, USA
¹⁶ Department of Physics and Astronomy, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
¹⁷ Cosmic Dawn Center (DAWN), Jagtvej 128, 2200 Copenhagen, N, Denmark
¹⁸ DTU-Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
¹⁹ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
²⁰ National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warsaw, Poland
²¹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy

Received: 18 December 2023
Accepted: 19 March 2024

Abstract

Aims. Measurements of the size of dust continuum emission are an important tool for constraining the spatial extent of star formation, and hence the buildup of stellar mass. Compact dust emission has generally been observed at cosmic noon (z ∼ 2 − 3). However, at earlier epochs, toward the end of the reionization (z ∼ 4 − 6), only the sizes of a handful of infrared (IR) bright galaxies have been measured. In this work, we derive the dust emission sizes of main-sequence (MS) galaxies at z ∼ 5 from the ALPINE survey.

Methods. We measured the dust effective radius, r_e, FIR, in the uv-plane in Band 7 of ALMA for seven ALPINE galaxies with resolved emission and we compared it with rest-frame ultraviolet (UV) and [CII]158 μm measurements. We studied the r_e, FIR − L_IR scaling relation by considering our dust size measurements and all the data in the literature at z ∼ 4 − 6. Finally, we compared our size measurements with predictions from simulations.

Results. The dust emission in the selected ALPINE galaxies is rather extended (r_e, FIR ∼ 1.5 − 3 kpc), similar to [CII]158 μm but a factor of ∼2 larger than the rest-frame UV emission. Putting together all the measurements at z ∼ 5, spanning two decades in luminosity from L_IR ∼ 10¹¹ L_⊙ to L_IR ∼ 10¹³ L_⊙, the data highlight a steeply increasing trend of the r_e, FIR − L_IR relation at L_IR < 10¹² L_⊙, followed by a downturn and a decreasing trend at brighter luminosities. Finally, simulations that extend up to the stellar masses of the ALPINE galaxies considered in the present work predict a subset of galaxies (∼25% at 10¹⁰ M_⊙ < M_⋆ < 10¹¹ M_⊙) with sizes as large as those measured.