HyperLEDA documentation: parameter: Mg2

The central Mg2 Lick index is an indicator of the composition of a stellar population. It depends both on the age and on the metallicity of the object. The measured Mg2 index corresponds to a certain defined region of the object and, after systematic corrections applied to series of measurements, it is reduced to a common standard aperture (for galaxies only).
The compilation of Mg2 measurements may be accessed in HyperLeda.
mg2 is the Mg2 index in mag.

The Mg2, as well as velocity dispersions, are standardized to an aperture r_norm of 0.595 h^-1kpc, which is equivalent to an angular diameter of 3.4 arcsec at the distance of Coma. The method of normalization is the one introduced by Jorgensen et al.

Central Mg2 Lick index for stellar systems