A new scaling relation for HII regions in spiral galaxies:
unveiling the true nature of the mass-metallicity relation

3D representation of the local surface mass density ΣLum, gas metallicity 12+log(O/H) and EW(Hα) relation. The size and color scaling of the data points are linked to the value of ΣLum, i.e. low-blue to high-red values. The projection of the data over any pair of axes reduces to the local M-Z, M-EW(Hα), and Z-EW(Hα) relations.

Figure adapted from: Rosales-Ortega et al. (2012) ApJL