Ellipticals: core-Sérsic vs Nuker

Mathematics – Logic

Scientific paper

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Scientific paper

HST has given the first look at elliptical galaxies on scales <1". Lauer et al (1995) used the Wide Field Planetary Camera (WFPC -1) to map the intensity of light I(r) in the inner 10" of 45 type E and S0 galaxies. They discovered that about 40% of the 39 ellipticals could not be described by a single power law. These galaxies have a core region where the power law I ∝ r-γ is less steep than the outer region I ∝ r-β . The resulting Nuker law allows for a smooth transition between these regions at a break radius rb. The physical rb varies widely: 30 pc < rb < 1200 pc. Rest et al (2001) used WFPC -2 to confirm the original WFPC -1 results with additional galaxies.
Using the full WFPC -2 mosaic, Trujillo, Erwin, Ramos, and Graham (2004) have extended the angular range of Rest et al by a factor between 3 and 8. They find that the extended outer region is incompatible with a Nuker law. Rather the power law for the outer region must be replaced by the Sérsic law, I(r) ∝ e-bn r1/n. They also find that the break radius is generally much reduced. Their published study of 9 core-Sérsic galaxies has 20 pc< rb <150 pc.
The new range of rb fits well within 1 wavelength λ of the non-Newtonian sinusoidal gravity. Here the potential of a point mass is GM cos(2 π r/λ )/r and λ =425 pc. (Bartlett 2001, 2004). With this gravity, the potential towards the center of any spherical mass distribution varies as ± sin(2 π r/λ )/r. I identify the + sign with the core-Sérsic galaxies and the - sign with the pure Sérsic galaxies. I will relate Sérsic's n to cosmological time t.

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