Statistical stellar mass corrections for high-z galaxies observed with
  JWST broad-band filters due to template degeneracies
  Stellar masses in future James Webb Space Telescope (JWST) deep blank-fields
will be mainly derived fitting the spectral energy distribution with
theoretical galaxy templates. We investigate the uncertainties and biases of
the stellar masses derived by using the LePhare code for spectral energy
distribution fitting and the Yggdrasil theoretical templates. We consider a
sample of mock galaxies at z$=$7-10 with mock JWST observations with
S/N$_{F150W}\geqslant$ 10. Our goal is to provide a list of statistical stellar
mass corrections to include on the stellar mass derivation for different output
galaxy properties and JWST filter combinations to correct for template
degeneracies. Median statistical stellar mass corrections vary from -0.83 dex
to 0.87 dex, while 25$\%$ (75$\%$) quartiles range from -0.83 dex (-0.67 dex)
to 0.51 dex (0.88 dex), depending on filter combinations and galaxy models. The
most challenging cases are galaxies with nebular emission lines, especially the
ones that are wrongly identified as galaxies without, relative dust-free
galaxies and galaxies with small metallicities (i.e. Z$=1/50Z_{\odot}$). The
stellar mass estimation of galaxies correctly identified without emission lines
is generally fine, except at z$=$10 when considering only the 8 NIRCam bands,
which make the MIRI bands very valuable. We have tested our stellar mass
corrections using the public JAGUAR galaxy catalogue, deriving that the average
discrepancy in the recovered stellar mass distribution decreases by 20-50$\%$
at z$>$7 after the correction. We found that without the stellar-mass
corrections the number of low-mass galaxies (M$^{*}<10^{7}M_{\odot}$) is
overestimated, which can potentially lead to systematic errors in the
calculation of the galaxy stellar mass function faint-end slope at high z.
