Stacked spectro-photometry for two groups of galaxies that have been photometrically selected (see Sect. 3.3). The photometric data includes EuclidYJH and the Vera C. Rubin Observatory ugrizy bands and the spectrocscopic data is from the Euclid NISP instrument with simulated noise. The photometric bandpasses used in the analysis are over-plotted. In both plots the photometric uncertainty bars are smaller than the markers. Left: an example stack for a group of galaxies with mean redshift z = 1.10. The stack includes 2 × 10³ galaxies. Right: stacked flux for a group at mean redshift z = 1.44 with 2 × 10⁶ galaxies.