Radial Migration of the Galactic Disk Based on Super Metal-rich Stars in the APOGEE Survey

Super metal-rich stars withFe/H>0.2 dex are selected from APOGEE DR14, their kinematical parameters, spatial velocities and orbital parameters are calculated based on Gaia DR2 data. The birth sites are estimated from metallicity and age. It is found that most of super metal-rich stars belong to the thin disk based on their lowα/Fe ratios and they undergo radial migration with 95.9% stars caused by churning and 50.5% stars by blurring. Migration distances due to churning peak at 2-5 kpc, which is larger than that caused by blurring(with a peak of 1-2 kpc). Thus, churning dominates (over blurring) during the evolution of the Galactic thin disk. It is found that migration distance due to churning increases with guiding radius when the sample is divided into different regions representing the inner disk, solar neighborhood and the outer disk. We propose a reasonable picture to explain these results as follows. Based on the N-body-chemo-dynamical model by Minchev et al, the bar's corotation resonance (at 4.7 kpc) can bring these stars from their birth sites (3-5 kpc) to solar neighborhood of 7-9 kpc. Then some super metal-rich stars are further accelerated at the 2:1 outer Lindblad resonance region (at 7.5 kpc) and migrated outward by 4-8 kpc, reaching the outer disk (10 kpc and beyond). Finally, we confirm the existence of young super metal-rich stars with age less than 1.0 gigayear in the APOGEE data. Since their migration rate is much higher than that predicted by the bar model, other mechanisms of radial migration should be introduced to explain their behaviors.