Simultaneous spectroscopic and photometric analysis of galaxies with
  STARLIGHT: CALIFA $+$ GALEX
  We present an extended version of the spectral synthesis code STARLIGHT
designed to incorporate both $\lambda$-by-$\lambda$ spectra and photometric
fluxes in the estimation of stellar population properties of galaxies. The code
is tested with simulations and data for 260 galaxies culled from the CALIFA
survey, spatially matching the 3700--7000 \AA\ optical datacubes to GALEX near
and far UV images. The sample spans E--Sd galaxies with masses from $10^9$ to
$10^{12} M_\odot$ and stellar populations all the way from star-forming to old,
passive systems. Comparing results derived from purely optical fits with those
which also consider the NUV and FUV data we find that: (1) The new code is
capable of matching the input UV data within the errors while keeping the
quality of the optical fit essentially unchanged. (2) Despite being unreliable
predictors of the UV fluxes, purely optical fits yield stellar population
properties which agree well with those obtained in optical+UV fits for nearly
90% of our sample. (3) The addition of UV constraints has little impact on
properties such as stellar mass and dust optical depth. Mean stellar ages and
metallicities also remain nearly the same for most galaxies, the exception
being low-mass, late-type galaxies, which become older and less enriched due to
rearrangements of their youngest populations. (4) The revised ages are better
correlated with observables such as the 4000 \AA\ break index, and the $NUV -
r$ and $u - r$ colours, an empirical indication that the addition of UV
constraints helps mitigating the effects of age-metallicity-extinction
degeneracies.
