Top left: Density plot of the H line-depth against line-width as identified by linefinder for all sources within 500 pc with Gaia DR3 XP spectra available. Dashed red lines indicate the thresholds in line-width and line-depth used to filter non-real H emitters (see Appendix B). Sources with width_lf > 25 nm are mostly M-dwarf contaminants. Sources with depth_lf < 10⁻¹⁷ W/nm/m² have emission comparable to the linefinder uncertainties. Top right: ‘accuracy’, ‘completeness’, ‘F₁-score’, and ‘F_β-score’ metrics as a function of pEW threshold for selecting H emitters. Vertical lines indicate the main thresholds used in this work (pEW <  − 0.5, and <  − 1.0 nm). Middle panels: Density plots of the H line-depth against line-width as identified by linefinder for all sources within 500 pc with Gaia DR3 XP spectra available and pEW <  − 0.5 nm (left) or pEW <  − 1.0 nm (right). Bottom panel: Plot of the fraction of contaminants against pEW threshold applied, where the number of contaminants is defined as the number of sources with with width_lf > 25 nm.