CEERS: MIRI deciphers the spatial distribution of dust-obscured star formation in galaxies at 0.1 < z < 2.5

¹ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
e-mail: benjamin.magnelli@cea.fr
² Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
³ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁴ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
⁵ Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
⁶ Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109-1107, USA
⁷ Aix-Marseille Univ., CNRS, CNES, LAM, 38 rue Joliot-Curie, 13388 Marseille, France
⁸ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁹ Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
¹⁰ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro #8701, Ex-Hda. San José de la Huerta, Morelia, Michoacán, México CP 58089, Mexico
¹¹ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
¹² Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
¹³ ESA/AURA Space Telescope Science Institute, Baltimore, MD, USA
¹⁴ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁵ Cavendish Laboratory, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK
¹⁶ Department of Physics and Astronomy, University of California, 900 University Ave, Riverside, CA 92521, USA
¹⁷ Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK
¹⁸ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
¹⁹ SRON Netherlands Institute for Space Research, Postbus 800, 9700 AV Groningen, The Netherlands
²⁰ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 30 May 2023
Accepted: 19 August 2023

Abstract

Aims. We study the stellar (i.e., rest-optical) and dust-obscured star-forming (i.e., rest-mid-infrared) morphologies (i.e., sizes and Sérsic indices) of star-forming galaxies (SFGs) at 0.1 < z < 2.5.

Methods. We combined Hubble Space Telescope (HST) images from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) with JWST images from the Cosmic Evolution Early Release Science (CEERS) survey to measure the stellar and dust-obscured star formation distributions of 69 SFGs. Rest-mid-infrared (rest-MIR) morphologies were determined using a Markov chain Monte Carlo (MCMC) approach applied to the sharpest Mid-InfraRed Instrument (MIRI) images (i.e., shortest wavelength) dominated by dust emission (S_ν^dust/S_ν^total > 75%), as inferred for each galaxy from our optical-to-far-infrared spectral energy distribution fits with CIGALE. Rest-MIR Sérsic indices were only measured for the brightest MIRI sources, that is, with a signal-to-noise (S/N) greater than 75 (35 galaxies). At a lower S/N, simulations do indeed show that simultaneous measurements of both the size and Sérsic index become less reliable. We extended our study to fainter sources (i.e., S/N > 10; 69 galaxies) by restricting our structural analysis to their rest-MIR sizes (Re_MIR) and by fixing their Sérsic index to a value of one.

Results. Our MIRI-selected sample corresponds to a mass-complete sample (> 80%) of SFGs down to stellar masses 10^9.5, 10^9.5, and 10¹⁰ M_⊙ at z ∼ 0.3, 1, and 2, respectively. The rest-MIR Sérsic index of bright galaxies (S/N > 75) has a median value of 0.7_−0.3^+0.8 (the range corresponds to the 16th and 84th percentiles), which is in good agreement with their median rest-optical Sérsic indices. The Sérsic indices as well as the distribution of the axis ratio of these galaxies suggest that they have a disk-like morphology in the rest-MIR. Galaxies above the main sequence (MS) of star formation (i.e., starbursts) have rest-MIR sizes that are, on average, a factor ∼2 smaller than their rest-optical sizes (Re_Opt.). The median rest-optical to rest-MIR size ratio of MS galaxies increases with their stellar mass, from 1.1_−0.2^+0.4 at ∼10^9.8 M_⊙ to 1.6_−0.3^+1.0 at ∼10¹¹ M_⊙. This mass-dependent trend resembles the one found in the literature between the rest-optical and rest-near-infrared sizes of SFGs, suggesting that it is primarily due to radial color gradients affecting rest-optical sizes and that the sizes of the stellar and star-forming components of SFGs are, on average, consistent at all masses. There is, however, a small population of SFGs (∼15%) with a compact star-forming component embedded in a larger stellar structure, with Re_Opt.^c > 1.8 × Re_MIR. This population could be the missing link between galaxies with an extended stellar component and those with a compact stellar component, the so-called blue nuggets.