Analysis of the Intrinsic Mid-Infrared L-band to Visible--Near-Infrared
  Flux Ratios in Spectral Synthesis Models of Composite Stellar Populations
  We analyze the intrinsic flux ratios of various visible--near-infrared
filters with respect to 3.5micron for simple and composite stellar populations,
and their dependence on age, metallicity and star formation history. UV/optical
light from stars is reddened and attenuated by dust, where different sightlines
across a galaxy suffer varying amounts of extinction. Tamura et al. (2009)
developed an approximate method to correct for dust extinction on a
pixel-by-pixel basis, dubbed the "beta_V" method, by comparing the observed
flux ratio to an empirical estimate of the intrinsic ratio of visible and
~3.5micron data. Through extensive modeling, we aim to validate the "beta_V"
method for various filters spanning the visible through near-infrared
wavelength range, for a wide variety of simple and composite stellar
populations. Combining Starburst99 and BC03 models, we built spectral energy
distributions (SEDs) of simple (SSP) and composite (CSP) stellar populations
for various realistic star formation histories (SFHs), while taking metallicity
evolution into account. We convolve various 0.44--1.65micron filter throughput
curves with each model SED to obtain intrinsic flux ratios beta_{lam,0}. When
unconstrained in redshift, the total allowed range of beta_{V,0} is 0.6--4.7,
or almost a factor of eight. At known redshifts, and in particular at low
redshifts (z<0.01), beta_{V,0} is predicted to span a narrow range of 0.6--1.9,
especially for early-type galaxies (0.6--0.7), and is consistent with observed
beta_V values. The beta_lam method can therefore serve as a first-order dust
correction method for large galaxy surveys that combine JWST (rest-frame
3.5micron) and HST (rest-frame visible--near-IR) data.
