Local Stellar Kinematics from RAVE data-VII. Metallicity Gradients from Red Clump Stars

Abstract

We investigate the Milky Way Galaxy's radial and vertical metallicity gradients using a sample of 47 406 red clump stars from the RAdial Velocity Experiment Data Release 4. Distances are calculated by adopting K-s-band absolute magnitude as -1.54 +/- 0.04 mag for the sample. The metallicity gradients are calculated with their current orbital positions (R-gc and Z) and with their orbital properties (R-m and z(max)): d[Fe/H]/ dR(gc) = -0.047 +/- 0.003 dex kpc(-1) for vertical bar Z vertical bar <= 0.5 kpc and d[Fe/H]/dR(m) = -0.025 +/- 0.002 dex kpc(-1) for z(max) <= 0.5 kpc. This reaffirms the radial metallicity gradient in the thin disc but highlights that gradients are sensitive to the selection effects caused by the difference between R-gc and R-m. The radial gradient is flat in the distance interval 0.5-1 kpc from the plane and then becomes positive greater than 1 kpc from the plane. The radial metallicity gradients are also eccentricity dependent. We showed that d[Fe/H]/dR(m) = -0.089 +/- 0.010, -0.073 +/- 0.007, -0.053 +/- 0.004 and -0.044 +/- 0.002 dex kpc(-1) for e(p) <= 0.05, e(p) <= 0.07, e(p) <= 0.10 and e(p) <= 0.20 sub-samples, respectively, in the distance interval z(max) <= 0.5 kpc. Similar trend is found for vertical metallicity gradients. Both the radial and vertical metallicity gradients are found to become shallower as the eccentricity of the sample increases. These findings can be used to constrain different formation scenarios of the thick and thin discs.