James Webb Space Telescope Feed Post

CEERS: 7.7 µm PAH Star Formation Rate Calibration with JWST MIRI

Each panel shows an example of the best-fit SEDs from CIGALE for sources in the selected sample in order of increasing redshift (top to bottom). The data in each plot show the measured flux densities with each curves representing different model components (see panel legend). The location of the observed 7.7 µm feature is highlighted in each panel by the purple arrow. To the right of each panel are 10'' ×10'' postage stamps of the CEERS HST F160W (top), composite RGB image of JWST/MIRI F1000W (B) + F1280W (G) + F1500W (R)(middle), composite RGB image of JWST/MIRI F1500W (B) + F1800W (G) + F2100W (R) (bottom). The MIRI images shift in color as the 7.7 µm PAH feature redshifts through the different MIRI bands. At z = 0.32, the 7.7 µm PAH feature falls in the F1000W band, with an additional PAH feature that peaks at F1500W which makes the image ”purple”. At z = 1.02, the 7.7 µm PAH feature falls in the F1500W band, making the middle image “red” and the bottom image “blue”. At z = 2.0, the PAH feature falls in the F2100W band, making the bottom image “red”. Abstract: We test the relationship between UV-derived star formation rates (SFRs) and the 7.7 µm polycyclic aromatic hydrocarbon (PAH) luminosities from the integrated emission of galaxies at z ~ 0 - 2. We utilize multi-band photometry covering 0.2 - 160 µm from HST, CFHT, JWST, Spitzer, and Herschel for galaxies in the Cosmic Evolution Early Release Science (CEERS) Survey. We perform spectral energy distribution (SED) modeling of these data to measure dust-corrected far-UV (FUV) luminosities, LFUV, and UV-derived SFRs. We then fit SED models to the JWST/MIRI 7.7 - 21 µm CEERS data to derive rest-frame 7.7 µm luminosities, L770, using the average flux density in the rest-frame MIRI F770W bandpass. We observe a correlation between L770 and LFUV, where log L770 is proportional to (1.27+/-0.04) log LFUV. L770 diverges from this relation for galaxies at lower metallicities, lower dust obscuration, and for galaxies dominated by evolved stellar populations. We derive a "single-wavelength" SFR calibration for L770 which has a scatter from model estimated SFRs (s?SFR) of 0.24 dex. We derive a "multi-wavelength" calibration for the linear combination of the observed FUV luminosity (uncorrected for dust) and the rest-frame 7.7 µm luminosity, which has a scatter of s?SFR = 0.21 dex. The relatively small decrease in s suggests this is near the systematic accuracy of the total SFRs using either calibration. These results demonstrate that the rest-frame 7.7 µm emission constrained by JWST/MIRI is a tracer of the SFR for distant galaxies to this accuracy, provided the galaxies are dominated by star-formation with moderate-to-high levels of attenuation and metallicity.