The Impact Of JWST Broadband Filter Choice On Photometric Redshift Estimation

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 l > 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 l < 0.6 mm , 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 l < 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 zphot quality significantly degrades at SN 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

The SCUBA HAlf degree extragalactic survey - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies

Determining an accurate position for a submillimetre (submm) galaxy (SMG) is the crucial step that enables us to move from the basic properties of an SMG sample – source counts and 2D clustering – to an assessment of their detailed, multiwavelength properties, their contribution to the history of cosmic star formation and their links with present-day galaxy populations. In this paper, we identify robust radio and/or infrared (IR) counterparts, and hence accurate positions, for over two-thirds of the SCUBA HAlf-Degree Extragalactic Survey (SHADES) Source Catalogue, presenting optical, 24-μm and radio images of each SMG. Observed trends in identification rate have given no strong rationale for pruning the sample. Uncertainties in submm position are found to be consistent with theoretical expectations, with no evidence for significant additional sources of error. Employing the submm/radio redshift indicator, via a parametrization appropriate for radio-identified SMGs with spectroscopic redshifts, yields a median redshift of 2.8 for the radio-identified subset of SHADES, somewhat higher than the median spectroscopic redshift. We present a diagnostic colour–colour plot, exploiting Spitzer photometry, in which we identify regions commensurate with SMGs at very high redshift. Finally, we find that significantly more SMGs have multiple robust counterparts than would be expected by chance, indicative of physical associations. These multiple systems are most common amongst the brightest SMGs and are typically separated by 2–6 arcsec, Graphic at z∼ 2, consistent with early bursts seen in merger simulations