2016ApJS..227...19B

The determination of galaxy redshifts in the James Webb Space Telescope's (JWST) blank-field surveys will mostly rely on photometric estimates, based on the data provided by JWST's Near-Infrared Camera (NIRCam) at 0.6-5.0 µm and Mid Infrared Instrument (MIRI) at λ>5.0 \mum. In this work we analyze the impact of choosing different combinations of NIRCam and MIRI broadband filters (F070W to F770W), as well as having ancillary data at λ<0.6 \mum, on the derived photometric redshifts (z_phot) of a total of 5921 real and simulated galaxies, with known input redshifts z = 0-10. We found that observations at λ<0.6 \mum are necessary to control the contamination of high-z samples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the NIRCam data mitigates the absence of ancillary observations at λ<0.6 \mum and improves the redshift estimation. At z = 7-10, accurate z_phot can be obtained with the NIRCam broadbands alone when S/N\geqslant10, but the z_phot quality significantly degrades at S/N\leqslant5. Adding MIRI photometry with 1 mag brighter depth than the NIRCam depth allows for a redshift recovery of 83%-99%, depending on spectral energy distribution type, and its effect is particularly noteworthy for galaxies with nebular emission. The vast majority of NIRCam galaxies with [F150W] = 29 AB mag at z = 7-10 will be detected with MIRI at [F560W, F770W] < 28 mag if these sources are at least mildly evolved or have spectra with emission lines boosting the mid-infrared fluxes.