Sample selection. Distribution of sources in the redshift–stellar mass plane. The grey and green hexagons show the density distribution of SFGs and QGs, respectively. The horizontal line indicates the mass cut-off limit of log(M_*/M_⊙) > 9 introduced in our selection. The red circles show the position of the final QG sample, composed of 50 galaxies. The representative errorbars for our catalogue are shown in the top right corner.