The Impact of JWST Broadband Filter Choice on Photometric Redshift Estimation

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Bisigello, L.;Caputi, K. I.;Colina, L.;Le Fèvre, O.;Nørgaard-Nielsen, H. U.;Pérez-González, P. G.;Pye, J.;van der Werf, P.;Ilbert, O.;Grogin, N.;Koekemoer, A. 2016. The Impact of JWST Broadband Filter Choice on Photometric Redshift Estimation. Astrophysical Journal Supplement Series 227, 2, DOI: 10.3847/0067-0049/227/2/19

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 mu m and Mid Infrared Instrument (MIRI) at lambda > 5.0 mm. 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 lambda < 0.6 mu m, 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 lambda < 0.6 mm 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 l < 0.6 mm and improves the redshift estimation. At z = 7-10, accurate zphot can be obtained with the NIRCam broadbands alone when S/N >= 10, but the z(phot) quality significantly degrades atb S/N <= 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.

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