The ALHAMBRA survey: 2-D analysis of the stellar populations in massive
  early-type galaxies at z < 0.3
  We present a technique that permits the analysis of stellar population
gradients in a relatively low cost way compared to IFU surveys analyzing a
vastly larger samples as well as out to larger radii. We developed a technique
to analyze unresolved stellar populations of spatially resolved galaxies based
on photometric multi-filter surveys. We derived spatially resolved stellar
population properties and radial gradients by applying a Centroidal Voronoi
Tesselation and performing a multi-color photometry SED fitting. This technique
has been applied to a sample of 29 massive (M$_{\star}$ > 10$^{10.5}$
M$_{\odot}$), early-type galaxies at $z$ < 0.3 from the ALHAMBRA survey. We
produced detailed 2D maps of stellar population properties (age, metallicity
and extinction). Radial structures have been studied and luminosity-weighted
and mass-weighted gradients have been derived out to 2 - 3.5 R$_\mathrm{eff}$.
We find the gradients of early-type galaxies to be on average flat in age
($\nabla$log Age$_\mathrm{L}$ = 0.02 $\pm$ 0.06 dex/R$_\mathrm{eff})$ and
negative in metallicity ($\nabla$[Fe/H]$_\mathrm{L}$ = - 0.09 $\pm$ 0.06
dex/R$_\mathrm{eff}$). Overall, the extinction gradients are flat
($\nabla$A$_\mathrm{v}$ = - 0.03 $\pm$ 0.09 mag/R$_\mathrm{eff}$ ) with a wide
spread. These results are in agreement with previous studies that used standard
long-slit spectroscopy as well as with the most recent integral field unit
(IFU) studies. According to recent simulations, these results are consistent
with a scenario where early-type galaxies were formed through major mergers and
where their final gradients are driven by the older ages and higher metallicity
of the accreted systems. We demonstrate the scientific potential of
multi-filter photometry to explore the spatially resolved stellar populations
of local galaxies and confirm previous spectroscopic trends from a
complementary technique.
