CEERS: MIRI deciphers the spatial distribution of dust-obscured star formation in galaxies at 0.1 < <i>z</i> < 2.5
B. Magnelli, Carlos Gómez-Guijarro, D. Elbaz, E. Daddi, Casey Papovich, Lu Shen, Pablo Arrabal Haro, Micaela B. Bagley, Eric F. Bell, V. Buat, Luca Costantin, Mark Dickinson, Steven L. Finkelstein, Jonathan P. Gardner, Eric F. Jiménez-Andrade, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Yipeng Lyu, Pablo G. Pérez‐González, Nor Pirzkal, Sandro Tacchella, Alexander de la Vega, Stijn Wuyts, Guang Yang, L. Y. Aaron Yung, Jorge A. Zavala
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 10 10 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 ∼10 11 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.