$R_{\rm e}$, or not $R_{\rm e}$: Developing $R_5\equiv R_{-2}$ as a scale radius for galaxy sizes, masses, and mass-to-light ratios

The effective half-light radius $R_{\rm e}$ marks an arbitrary 50-per-cent light boundary, and scaling relations involving such effective radii and their associated surface brightnesses, $μ_{\rm e}$, depend systematically on the adopted…

The effective half-light radius $R_{\rm e}$ marks an arbitrary 50-per-cent light boundary, and scaling relations involving such effective radii and their associated surface brightnesses, $μ_{\rm e}$, depend systematically on the adopted percentage. Here, a gradient-defined…