Stromgren photometry of Galactic Globular Clusters. II Metallicity distribution of red giants in Omega Centauri

We present new intermediate-band Stroemgren photometry based on more than 300 u,v,b,y images of the Galactic globular cluster Omega Cen. Optical data were supplemented with new multiband near-infrared (NIR) photometry (350 J,H,K_s images). The final optical-NIR catalog covers a region of more than 20*20 arcmin squared across the cluster center. We use different optical-NIR color-color planes together with proper motion data available in the literature to identify candidate cluster red giant (RG) stars. By adopting different Stroemgren metallicity indices we estimate the photometric metallicity for ~4,000 RGs, the largest sample ever collected. The metallicity distributions show multiple peaks ([Fe/H]_phot=-1.73+/-0.08,-1.29+/-0.03,-1.05+/-0.02,-0.80+/-0.04,-0.42+/-0.12 and -0.07+/-0.08 dex) and a sharp cut-off in the metal-poor tail ([Fe/H]_phot -1.7 dex).