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Arxiv: High-z stellar masses can be recovered robustly with JWST photometry Published: 12/3/2024 7:50:49 PM Updated: 12/3/2024 7:50:49 PM

Paper abstract: Robust inference of galaxy stellar masses from photometry is crucial forconstraints on galaxy assembly across cosmic time. Here, we test acommonly-used Spectral Energy Distribution (SED) fitting code, using simulatedgalaxies from the SPHINX20 cosmological radiation hydrodynamics simulation,with JWST NIRCam photometry forward-modelled with radiative transfer. Fittingthe synthetic photometry with various star formation history models, we showthat recovered stellar masses are, encouragingly, generally robust to within afactor of ~3 for galaxies in the range M*~10^7-10^9M_sol at z=5-10. Theseresults are in stark contrast to recent work claiming that stellar masses canbe underestimated by as much as an order of magnitude in these mass andredshift ranges. However, while >90% of masses are recovered to within 0.5dex,there are notable systematic trends, with stellar masses typicallyoverestimated for low-mass galaxies (M*<~10^8M_sol) and slightly underestimatedfor high-mass galaxies (M*>~10^9M_sol). We demonstrate that these trends arisedue to the SED fitting code poorly modelling the impact of strong emissionlines on broadband photometry. These systematic trends, which exist for allstar formation history parametrisations tested, have a tilting effect on theinferred stellar mass function, with number densities of massive galaxiesunderestimated (particularly at the lowest redshifts studied) and numberdensities of lower-mass galaxies typically overestimated. Overall, this worksuggests that we should be optimistic about our ability to infer the masses ofhigh-z galaxies observed with JWST (notwithstanding contamination from AGN) butcareful when modelling the impact of strong emission lines on broadbandphotometry.