Upper panel: correlation of v_IS,comb, v_IS,Si IV and v_IS,Al III with the stellar mass M_⋆ for VANDELS star-forming galaxies selected in this work. The first two panels in each row show the relation for individual galaxies (red diamonds), while the black empty squares are the median v_IS in bins of increasing M_⋆. The red horizontal continuous line shows the median v_IS for the entire sample shown in each plot, while the red shaded regions highlight the standard deviation of all the ISM shift values. The last panel of the row shows the velocity shifts calculated directly from the spectral stacks in four bins of stellar mass. Lower panel: same as above but as a function of the SFR.