Local Stellar Kinematics from RAVE data -- VIII. Effects of the Galactic Disc Perturbations on Stellar Orbits of Red Clump Stars

TL;DR

This study investigates how Galactic disc perturbations influence stellar orbits and metallicity gradients of red clump stars, revealing that resonances significantly affect the observed metallicity distribution in the Milky Way.

Contribution

It introduces a detailed analysis of stellar orbit properties considering non-axisymmetric Galactic potential models, highlighting the impact of resonances on metallicity gradients.

Findings

Radial metallicity gradients vary with orbital eccentricity and vertical distance from the Galactic plane.

Resonance regions, especially the outer Lindblad resonance, significantly influence metallicity gradient measurements.

No radial metallicity gradient is observed in the thick disc, contrasting with the thin disc results.

Abstract

We aim to probe the dynamic structure of the extended Solar neighbourhood by calculating the radial metallicity gradients from orbit properties, which are obtained for axisymmetric and non-axisymmetric potential models, of red clump (RC) stars selected from the RAdial Velocity Experiment's Fourth Data Release. Distances are obtained by assuming a single absolute magnitude value in near-infrared, i.e. $M_{Ks}=-1.54\pm0.04$ mag, for each RC star. Stellar orbit parameters are calculated by using the potential functions: (i) for the MWPotential2014 potential, (ii) for the same potential with perturbation functions of the Galactic bar and transient spiral arms. The stellar age is calculated with a method based on Bayesian statistics. The radial metallicity gradients are evaluated based on the maximum vertical distance ($z_{max}$) from the Galactic plane and the planar eccentricity ($e_p$) of RC stars for both of the potential models. The largest radial metallicity gradient in the $0<z_{max} \leq0.5$ kpc distance interval is $-0.065\pm0.005$ dex kpc$^{-1}$ for a subsample with $e_p\leq0.1$, while the lowest value is $-0.014\pm0.006$ dex kpc$^{-1}$ for the subsample with $e_p\leq0.5$. We find that at $z_{max}>1$ kpc, the radial metallicity gradients have zero or positive values and they do not depend on $e_p$ subsamples. There is a large radial metallicity gradient for thin disc, but no radial gradient found for thick disc. Moreover, the largest radial metallicity gradients are obtained where the outer Lindblad resonance region is effective. We claim that this apparent change in radial metallicity gradients in the thin disc is a result of orbital perturbation originating from the existing resonance regions.