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

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jats:pjats:italicAims.</jats:italic> 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 < jats:italicz</jats:italic> < 2.5.</jats:p> jats:pjats:italicMethods.</jats:italic> We combined jats:italicHubble</jats:italic> 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 (jats:italicS</jats:italic>jats:subjats:italicν</jats:italic></jats:sub>jats:supdust</jats:sup>/jats:italicS</jats:italic>jats:subjats:italicν</jats:italic></jats:sub>jats:suptotal</jats:sup> > 75%), as inferred for each galaxy from our optical-to-far-infrared spectral energy distribution fits with jats:monospaceCIGALE</jats:monospace>. 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., jats:italicS</jats:italic>/jats:italicN</jats:italic> > 10; 69 galaxies) by restricting our structural analysis to their rest-MIR sizes (jats:italicRe</jats:italic>jats:subMIR</jats:sub>) and by fixing their Sérsic index to a value of one.</jats:p> jats:pjats:italicResults.</jats:italic> Our MIRI-selected sample corresponds to a mass-complete sample (> 80%) of SFGs down to stellar masses 10jats:sup9.5</jats:sup>, 10jats:sup9.5</jats:sup>, and 10jats:sup10</jats:sup> jats:italicM</jats:italic>jats:sub⊙</jats:sub> at jats:italicz</jats:italic> ∼ 0.3, 1, and 2, respectively. The rest-MIR Sérsic index of bright galaxies (jats:italicS</jats:italic>/jats:italicN</jats:italic> > 75) has a median value of 0.7jats:sub−0.3</jats:sub>jats:sup+0.8</jats:sup> (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 (jats:italicRe</jats:italic>jats:subOpt.</jats:sub>). The median rest-optical to rest-MIR size ratio of MS galaxies increases with their stellar mass, from 1.1jats:sub−0.2</jats:sub>jats:sup+0.4</jats:sup> at ∼10jats:sup9.8</jats:sup> jats:italicM</jats:italic>jats:sub⊙</jats:sub> to 1.6jats:sub−0.3</jats:sub>jats:sup+1.0</jats:sup> at ∼10jats:sup11</jats:sup> jats:italicM</jats:italic>jats:sub⊙</jats:sub>. 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 Rejats:subOpt.</jats:sub>jats:supc</jats:sup> > 1.8 × Rejats:subMIR</jats:sub>. 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.</jats:p>



5109 Space Sciences, 51 Physical Sciences

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Astronomy and Astrophysics

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EDP Sciences