2021ApJ...908..144Y

The James Webb Space Telescope MIRI instrument will revolutionize extragalactic astronomy with unprecedented sensitivity and angular resolution in mid-IR. Here we assess the potential of MIRI photometry to constrain galaxy properties in the Cosmic Evolution Early Release Science (CEERS) survey. We derive estimated MIRI fluxes from the spectral energy distributions (SEDs) of real sources that fall in a planned MIRI pointing. We also obtain MIRI fluxes for hypothetical active galactic nucleus (AGN)-galaxy mixed models varying the AGN fractional contribution to the total IR luminosity (frac_AGN). Based on these model fluxes, we simulate CEERS imaging (3.6 hr exposure) in six bands from F770W to F2100W using MIRISIM and reduce these data using JWST PIPELINE. We perform point-spread-function-matched photometry with TPHOT and fit the source SEDs with X-CIGALE, simultaneously modeling photometric redshift and other physical properties. Adding the MIRI data, the accuracy of both redshift and frac_AGN is generally improved by factors of >=2 for all sources at z <= 3. Notably, for pure-galaxy inputs (frac_AGN = 0), the accuracy of frac_AGN is improved by ∼100 times thanks to MIRI. The simulated CEERS MIRI data are slightly more sensitive to AGN detections than the deepest X-ray survey, based on the empirical L_X-L_6 µm_ relation. Like X-ray observations, MIRI can also be used to constrain the AGN accretion power (accuracy ≃0.3 dex). Our work demonstrates that MIRI will be able to place strong constraints on the mid-IR luminosities from star formation and AGNs and thereby facilitate studies of the galaxy/AGN coevolution.