Online material

Appendix A: Gradients with respect to (R,  z)

In order to estimate the effect of “blurring” and the influence of orbital parameter uncertainties on our measured abundance gradients, we also computed the [M/H] and [α/M] abundance gradients with respect to the current Galactocentric distance R, for different bins in current distance from the Galactic plane z. The results are shown in Fig. A.1.

Since provides a more direct observable than , which depends also weakly on the adopted Galactic potential and are influenced by subtle volume-based kinematic biases (see Boeche et al. 2013b, for a discussion), it is useful to compare the two different gradient measurements.

It is also worth noting that our results on the abundance gradients compare very well with the findings of Hayden et al. (2013), who use a different set of spectrophotometric distances (Hayden et al., in prep.) for their APOGEE sample. The gradient measured by Hayden et al., using our adopted vertical and radial ranges, is compatible with the values we obtain in Fig. A.1. For stars with 6 <R < 11 and 0 <z < 0.4 kpc, the authors also obtain a gradient of dex/kpc. As the authors limit their analysis to smaller distances from the plane, they do not find a positive radial [M/H] gradient at large heights.

As discussed in Sect. 4.2.3, future work using more APOGEE data will certainly help to understand and resolve the discrepancies seen between Figs. 15, 16 and A.1.

	Fig. A.1 Top: radial metallicity gradients (left, using now the current Galactocentric distance R) and metallicity distribution functions (right) for the HQ sample, in different ranges of Galactic height z. Bottom: same as above but for the [α/M] gradients and corresponding distribution functions.
Open with DEXTER

© ESO, 2014