Central Mg2 Lick index for stellar systems
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.
is the Mg2 index in mag.
The Mg2, as well as velocity dispersions, are standardized to
an aperture rnorm
of 0.595 h-1kpc, which is equivalent to an angular diameter
3.4 arcsec at the distance of Coma. The method of normalization is the
one introduced by Jorgensen et al.