In section 5. Galactic structure, stellar clusters and population
Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way
Large spectroscopic Galactic surveys all undergo a selection process for choosing their targets. This selection function can alter the final form of the metallicity distribution function and the vertical metallicity gradient differently for different surveys. This paper investigates the effects of the selection functions on metallicity trends in the common fields between the APOGEE, LAMOST, RAVE, and Gaia-ESO surveys. The authors use the stellar population synthesis models GALAXIA and TRILEGAL to create mock fields for each survey and apply the selection function in the form of colour and magnitude cuts to replicate the observed sample and investigate the effects of the different selection functions. They find that the selection function has a negligible effect on the metallicity distribution function or the vertical metallicity gradients for the APOGEE, LAMOST, and RAVE surveys. The corrected vertical metallicity gradients between the four surveys are consistent within 1-σ. It is, therefore, possible to combine common fields of these different surveys provided that their metallicities are on the same scale.