Local stellar kinematics from RAVE data: III. Radial and Vertical Metallicity Gradients based on Red Clump Stars

TL;DR

This study analyzes metallicity gradients in the Milky Way's thin and thick discs using RAVE red clump stars, revealing similar radial gradients but steeper vertical gradients for thin disc stars, informing galaxy formation models.

Contribution

It provides new measurements of radial and vertical metallicity gradients for thin and thick disc stars based on RAVE data, utilizing probabilistic and dynamical population assignments.

Findings

Radial metallicity gradients are approximately -0.041 dex/kpc for thin disc stars.

Vertical metallicity gradients are steeper, around -0.109 to -0.260 dex/kpc, depending on population.

Thicker disc samples show shallower abundance gradients.

Abstract

We investigate radial and vertical metallicity gradients for a sample of red clump stars from the RAdial Velocity Experiment (RAVE) Data Release 3. We select a total of 6781 stars, using a selection of colour, surface gravity and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thin or thick disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We derive almost equal metallicity gradients as a function of Galactocentric distance for the high probability thin disc stars and for stars with vertical orbital eccentricities consistent with being dynamically young, e_v<=0.07, i.e. d[M/H]/dR_m = -0.041(0.003) and d[M/H]/dR_m = -0.041(0.007) dex/kpc. Metallicity gradients as a function of distance from the Galactic plane for the same populations are steeper, i.e. d[M/H]/dz_{max} = -0.109(0.008) and d[M/H]/dz_{max} = -0.260(0.031) dex/kpc, respectively. R_m and z_{max} are the arithmetic mean of the perigalactic and apogalactic distances, and the maximum distance to the Galactic plane, respectively. Samples including more thick disc red clump giant stars show systematically shallower abundance gradients. These findings can be used to distinguish between different formation scenarios of the thick and thin discs.