PAH Emission from Star-forming Galaxies in JWST Mid-infrared Imaging of the Lensing Cluster SMACS J0723.3-7327

Abstract

The mid-infrared spectra of star-forming galaxies (SFGs) are characterized by characteristic broad polycyclic aromatic hydrocarbon (PAH) emission features at 3–20 μm. As these features are redshifted, they are predicted to dominate the flux at specific mid-infrared wavelengths, leading to substantial redshift-dependent color variations in broadband photometry. The advent of JWST for the first time allows the study of this effect for normal SFGs. Based on spectral energy distribution templates, we here present tracks in mid-infrared (4.4, 7.7, 10, 15, and 18 μm) color–color diagrams describing the redshift dependence of SFG colors. In addition, we present simulated color–color diagrams by populating these tracks using the cosmic star formation history and the star formation rate function. Depending on redshift, we find that SFGs stand out in the color–color diagrams by several magnitudes. We provide the first observational demonstration of this effect for galaxies detected in the JWST Early Release Observations of the field toward the lensing cluster SMACS J0723.3−7327. While the distribution of detected galaxies is consistent with the simulations, the numbers are substantially boosted by lensing effects. The PAH emitter with the highest spectroscopic redshift, detected in all bands, is a multiply imaged galaxy at z = 1.45. There is also a substantial number of cluster members that do not exhibit PAH emission except for one SFG at z = 0.38. Future wider-field observations will further populate mid-infrared color–color diagrams and provide insight into the evolution of typical SFGs.

Little Red Dots or Brown Dwarfs? NIRSpec Discovery of Three Distant Brown Dwarfs Masquerading as NIRCam-selected Highly Reddened Active Galactic Nuclei

“…We reduced the NIRSpec prism data for the 14 targeted little red dots using the pipeline described in detail in Langeroodi & Hjorth (2023). In brief, we converted the raw data into count-rate images (the stage 1 reduction) using the 1.10.0 version of the official STScI JWST pipeline (Ferruit et al 2022;Bushouse et al 2023) and the jwst_1106.pmap Calibration Reference Data System (CRDS) context file.…”

“…We measured the multiband Hubble Space Telescope (HST) and NIRCam photometry of the 14 targeted little red dots using the pipeline detailed in Langeroodi & Hjorth (2023). The reduced images were acquired from the Grizli Image Release (v6.0) repository.…”

Constraining the AGN Luminosity Function from JWST with the X-Ray Background

“…Newer studies with JWST NIRSpec find comparable or higher UV LFs for the AGN at z ∼ 9 than at z ∼ 6 (Fujimoto et al 2023), with a 10%-15% AGN fraction in galaxies. Forthcoming spectroscopic census of AGN will help reveal the presence of other factors such as star formation driven outflows that may make a dominant contribution to the luminosity (Ferrara et al 2023;Matthee et al 2023;Zhang et al 2023) or objects such as brown dwarfs, which may account for up to a third of the AGN candidate sample (Greene et al 2023;Langeroodi et al 2023). (Harikane et al 2023).…”

A Framework for Modeling Polycyclic Aromatic Hydrocarbon Emission in Galaxy Evolution Simulations

“…With the launch of the JWST in 2021, observational studies of PAHs in galaxies are poised to enter a renaissance-already JWST is revealing the impact of galactic environment on PAH emission in galaxies near and far at unprecedented sensitivity and spatial resolution (e.g., Armus et al 2023;Chastenet et al 2022Chastenet et al , 2023Dale et al 2023;Egorov et al 2023;Evans 2022;Langeroodi & Hjorth 2023;Lai et al 2022;U et al 2022;Sandstrom et al 2023). What is missing thus far is a quantitative methodology for modeling the physical processes that drive the evolution of dust in the ISM in galaxies that span a wide range of physical conditions, and connecting these processes to the emergent PAH emission.…”