4.3 Photometry of Elliptical Galaxy

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4.3 Photometry of Elliptical Galaxy

• Skarma Kim

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Contents

• Radial surface-brightness profile
• - de Vaucouleurs R1/4 law
• - cD galaxies
• - Dwarf elliptical galaxies
• - Centers of elliptical galaxies

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Radial surface-brightness profile

• de Vaucouleurs R1/4 law

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de Vaucouleurs R1/4 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 Re.

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de Vaucouleurs R1/4 law

• The Parameter Ie is clearly the surface
  brightness at RRe, and, according to the R1/4
  law, the central brightness of the galaxy is
  103.33 Ie 2000 Ie.

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Box 4.1

• Three-Parameter Fitting Function
• - generalized de Vaucouleurs law
• - Hubble-Oemler law
• - Hubble law
• Figure 4.27

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de Vaucouleurs R1/4 law

• To some extent the deviations of galaxies from
  the R1/4 law depend systematically on the
  galaxies luminosities.

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cD galaxies
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cD galaxies

• Galaxies whose surface-brightness profiles turn
  strongly upwards in a plot are called cD galaxies.

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Dwarf elliptical galaxies

• Two classes
• Fig 4.30

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Compact dwarf elliptical
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Centers of elliptical galaxies

• Fig 4.31
• Fig 4.32