Reddening and metallicity maps of the Milky Way Bulge from VVV and
  2MASS. I.The method and minor axis maps
  We present a method to obtain reddening maps and to trace structure and
metallicity gradients of the bulge using data from the recently started ESO
public survey Vista Variables in the Via Lactea (VVV). We derive the mean J-Ks
color of the red clump (RC) giants in 1835 subfields in the Bulge region with
-8<b<-0.4 and 0.2<l<1.7, and compare it to the color of RC stars in Baade's
Window for which we adopt E(B-V)=0.55. This allows us to derive the reddening
map on a small enough scale to minimize the problems arising from differential
extinction. The dereddened magnitudes are then used to build the bulge
luminosity function in regions of 0.4 x 0.4 deg to obtain the mean RC
magnitudes. These are used as distance indicator in order to trace the bulge
structure. Finally, for each subfield we derive photometric metallicities
through interpolation of red giant branch colors on a set of empirical ridge
lines. The photometric metallicity distributions are compared to metallicity
distributions obtained from high resolution spectroscopy in the same regions.
The reddening determination is sensitive to small scale variations which are
clearly visible in our maps. The luminosity function clearly shows the double
RC recently discovered in 2MASS and OGLE III datasets, hence allowing to trace
the X-shape morphology of the bulge. Finally, the mean of the derived
photometric metallicity distributions are in remarkable agreement with those
obtained from spectroscopy. The VVV survey presents a unique tool to map the
bulge properties by means of the consistent method presented here. The
remarkable agreement between our results and those presented in literature for
the minor axis allows us to safely extend our method to the whole region
covered by the survey.
