The Impact of JWST Broadband Filter Choice on Photometric Redshift Estimation

Overview & Synopsis

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 μ {{m}}. 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 μ {{m}}, on the derived photometric redshifts (zphot) of a total of 5921 real and simulated galaxies, with known input redshifts z = 0-10. We found that observations at λ < 0.6 μ {{m}} 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 μ {{m}} and improves the redshift estimation. At z = 7-10, accurate zphot can be obtained with the NIRCam broadbands alone when {{S}}/{{N}}≥slant 10, but the zphot quality significantly degrades at {{S}}/{{N}}≤slant 5. 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.