.We present JWST/NIRCam observations of a strongly-lensed, sub-L∗, multiply-imaged galaxy at z = 6.072, with magnification factors μ ≳ 20
across the galaxy. The galaxy has rich HST, MUSE and ALMA ancillary observations across a broad wavelength range. Aiming to quantify the
reliability of stellar mass estimates of high redshift galaxies, we perform a spatially-resolved analysis of the physical properties at scales of ∼ 200 pc, inferred from SED modelling of 5 JWST/NIRCam imaging bands covering 0.16 μm < λrest < 0.63 μm on a pixel-by-pixel basis. We find young stars surrounded by extended older stellar populations. By comparing Hα+[N ii] and [O iii]+Hβ maps inferred from the image analysis with our additional NIRSpec IFU data, we find that the spatial distribution and strength of the line maps are in agreement with the IFU measurements.
We explore different parametric star formation history forms with Bagpipes on the spatially-integrated photometry, finding that a double power-law
star formation history retrieves the closest value to the spatially-resolved stellar mass estimate, and other SFH forms suffer from the dominant
outshining emission from the youngest stars, thus underestimating the stellar mass – up to ∼0.5 dex–. On the other hand, the DPL cannot match
the IFU measured emission lines. Additionally, the ionizing photon production efficiency may be overestimated in a spatially-integrated approach
by ∼0.15 dex, when compared to a spatially-resolved analysis. The agreement with the IFU measurements implies that our pixel-by-pixel results
derived from the broadband images are robust, and that the mass discrepancies we find with spatially-integrated estimates are not just an effect of SED-fitting degeneracies or lack of NIRCam coverage. Additionally, this agreement points towards the pixel-by-pixel approach as a way to
mitigate the general degeneracy between the flux excess from emission lines and underlying continuum, especially when lacking photometric
medium-band coverage and/or IFU observations. This study stresses the importance of studying galaxies as the complex systems that they are,
resolving their stellar populations when possible, or using more flexible SFH parameterisations. This can aid our understanding of the early stages
of galaxy evolution by addressing the challenge of inferring robust stellar masses and ionizing photon production efficiencies of high redshift
galaxies.
