Unresolved versus resolved: testing the validity of young simple stellar
  population models with VLT/MUSE observations of NGC 3603
  CONTEXT. Stellar populations are the building blocks of galaxies including
the Milky Way. The majority, if not all extragalactic studies are entangled
with the use of stellar population models given the unresolved nature of their
observation. Extragalactic systems contain multiple stellar populations with
complex star formation histories. However, their study is mainly based upon the
principles of simple stellar populations (SSP). Hence, it is critical to
examine the validity of SSP models. AIMS. This work aims to empirically test
the validity of SSP models. This is done by comparing SSP models against
observations of spatially resolved young stellar population in the
determination of its physical properties, i.e. age and metallicity. METHODS.
Integral field spectroscopy of a young stellar cluster in the Milky Way, NGC
3603, is used to study the properties of the cluster both as a resolved and
unresolved stellar population. The unresolved stellar population is analysed
using the H$\alpha$ equivalent width as an age indicator, and the ratio of
strong emission lines to infer metallicity. In addition, spectral energy
distribution (SED) fitting using STARLIGHT, is used to infer these properties
from the integrated spectrum. Independently, the resolved stellar population is
analysed using the color-magnitude diagram (CMD) for age and metallicity
determination. As the SSP model represents the unresolved stellar population,
the derived age and metallicity are put to test whether they agree with those
derived from resolved stars. RESULTS. The age and metallicity estimate of NGC
3603 derived from integrated spectroscopy are confirmed to be within the range
of those derived from the CMD of the resolved stellar population, including
other estimates found in the literature. The result from this pilot study
supports the reliability of SSP models for studying unresolved young stellar
populations.
