Panel a: same as Fig. 21c (kinematic selection VT > 200 km s−1) overlaid with PARSEC isochrones for [M/H] = − 1.3, age = 13 Gyr (blue), and [M/H] = − 0.5, age = 11 Gyr (magenta) and [α/Fe] = 0.23; green line: median spline fit to the main sequence of the thick-disk kinematic selection (Fig. 21b). Panel b: [α/Fe] vs. [Fe/H] of the corresponding APOGEE stars without extinction criterion applied. Panel c: density distribution of the tangential velocity VT on the blue and red sides of a median spline main-sequence fit.