RRab Lyrae metallicity gradient in the Galactic bulge

Abstract

Aims. We revisit the presence and significance of the Galactic bulge metallicity gradients, using the OGlE-III RR Lyrae sample. Methods. We implemented a Monte Carlo simulation to account for observational uncertainties and systematic errors to test the presence, significance, and spatial variation of RR Lyr photometric metallicity gradients within the Galactic bulge. Furthermore, we take special consideration to identify and account for possible observational and statistical biases, which may introduce an apparent metallicity gradient into the sample. Results. We find a mean Galactic bulge RRab metallicity of −0.97 ± 0.29 dex, a global radial metallicity gradient of −0.016 ± 0.008 dex Kpc-1 , and a global vertical metallicity gradient of −0.063 ± 0.013 dex Kpc-1 . Furthermore, neither the global radial nor vertical gradients can be explained by random chance, unjustified extrapolation of the metallicity calibration law, or induced by a Malmquist bias.