Imaging & Spectroscopy

PAH Emission From Star-forming Galaxies In JWST Mid-infrared Imaging Of The Lensing Cluster SMACS J0723.3−7327

By Keith Cowing
Press Release
October 13, 2022
Filed under , , , , , ,
PAH Emission From Star-forming Galaxies In JWST Mid-infrared Imaging Of The Lensing Cluster SMACS J0723.3−7327
F444W−F770W vs. F770W−F1000W color-color diagram for the JWST observations of the SMACS J0723 field. Top panel: Simulated diagram for SFGs detected (filled crosses) in a MIRI FOV with the same magnitude limits as those of the SMACS J0723 observations. The open circles in- dicate the entire sample of SFGs in this FOV, most of which are undetected. The shaded tracks (small filled circles) are similar to the tracks of Figure 1, with an additional 0.05 mag scatter. We expect to detect 18 SFGs per MIRI FOV. We identify 23 cluster galaxies with available spectroscopic redshifts (z = 0.387 ± 0.020; yellow-filled crosses). The only cluster galaxy that resembles the color-color diagram loca- tion of SFGs (yellow-filled cross at the upper region) is a Seyfert galaxy, mimicking the PAH emission of SFGs (see Section 5). astro-ph.GA

The mid-infrared spectra of star-forming galaxies (SFGs) are characterized by characteristic broad 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 broad-band 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 towards 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, which do not exhibit PAH emission, except for one Seyfert galaxy 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.

Danial Langeroodi, Jens Hjorth

Comments: 8 pages, 5 figures, Submitted to ApJL, Comments are Welcome!
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2210.06482 [astro-ph.GA] (or arXiv:2210.06482v1 [astro-ph.GA] for this version)
Submission history
From: Danial Langeroodi
[v1] Wed, 12 Oct 2022 18:00:00 UTC (4,662 KB)
Astrobiology, Astrochemistry

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