Same as Fig. 1, but plotting the metallicity profiles of ETGs stacked spectra as a function of velocity dispersion σ. The velocity dispersion of the M31 bulge (σ ∼ 150 km s⁻¹) is marked with a vertical gray arrow in both panels. The gray triangles with error bars, at σ ∼ 150 km s⁻¹ and σ ∼ 280 km s⁻¹, show the estimates of [Fe/H] and [M/H] obtained by mimicking the Sloan fiber aperture for low- and high-σ ETGs (see the text).