Panchromatic Averaged Stellar Populations: PaasP
  We study how the spectral fitting of galaxies, in terms of light fractions
derived in one spectral region translates into another region, by using results
from evolutionary synthesis models. In particular, we examine propagation
dependencies on Evolutionary Population Synthesis (EPS, {\sc grasil}, {\sc
galev}, Maraston and {\sc galaxev}) models, age, metallicity, and stellar
evolution tracks over the near-UV---near infrared (NUV---NIR, 3500\AA\ to
2.5\mc) spectral region. Our main results are: as expected, young ($t \lesssim$
400 Myr) stellar population fractions derived in the optical cannot be directly
compared to those derived in the NIR, and vice versa. In contrast, intermediate
to old age ($t \gtrsim$ 500 Myr) fractions are similar over the whole spectral
region studied. The metallicity has a negligible effect on the propagation of
the stellar population fractions derived from NUV --- NIR. The same applies to
the different EPS models, but restricted to the range between 3800 \AA\ and
9000 \AA. However, a discrepancy between {\sc galev}/Maraston and {\sc
grasil}/{\sc galaxev} models occurs in the NIR. Also, the initial mass function
(IMF) is not important for the synthesis propagation. Compared to {\sc
starlight} synthesis results, our propagation predictions agree at $\sim$95%
confidence level in the optical, and $\sim$85% in the NIR. {\bf In summary,
spectral fitting} performed in a restricted spectral range should not be
directly propagated from the NIR to the UV/Optical, or vice versa. We provide
equations and an on-line form ({\bf Pa}nchromatic {\bf A}veraged {\bf S}tellar
{\bf P}opulation - \paasp) to be used for this purpose.
