4.3 Photometry of Elliptical Galaxy Skarma Kim
Contents Radial surface-brightness profile - de Vaucouleurs R 1/4 law - cD galaxies - Dwarf elliptical galaxies - Centers of elliptical galaxies
Radial surface-brightness profile de Vaucouleurs R 1/4 law
The numerical factor 3.33 is chosen such that, if the galaxy image were circularly symmetric and if the formula were valid all radii, both large and small, then one-half of the total light of the system would be emitted interior to R e.
de Vaucouleurs R 1/4 law The Parameter I e is clearly the surface brightness at R=R e, and, according to the R 1/4 law, the central brightness of the galaxy is I e ~2000 I e.
Box 4.1 Three-Parameter Fitting Function - generalized de Vaucouleurs law - Hubble-Oemler law - Hubble law Figure 4.27
de Vaucouleurs R 1/4 law To some extent the deviations of galaxies from the R1/4 law depend systematically on the galaxies’ luminosities.
cD galaxies
Galaxies whose surface-brightness profiles turn strongly upwards in a plot are called cD galaxies.
Dwarf elliptical galaxies Two classes Fig 4.30
Compact dwarf elliptical
Centers of elliptical galaxies Fig 4.31 Fig 4.32