Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS

Aims. We investigate the large-scale metallicity distribution in the Galactic bulge using large spatial coverage to constrain the bulge formation scenario. Methods. We use the VISTA variables in the Via Lactea (VVV) survey data and 2MASS photometry, which cover 320 sqdeg of the Galactic bulge, to derive photometric metallicities by interpolating the (J − Ks)0 colors of individual red giant branch stars based on a set of globular cluster ridge lines. We then use this information to construct the first global metallicity map of the bulge with a resolution of 30′ × 45′. Results. The metallicity map of the bulge revealed a clear vertical metallicity gradient of ~0.04 dex/deg (~0.28 dex/kpc), with metal-rich stars ([Fe/H] ~ 0) dominating the inner bulge in regions closer to the Galactic plane (|b|