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Universality of galactic surface densities within one dark halo scale-length


It was recently discovered that the mean dark matter surface density within one dark halo scale-length (the radius within which the volume density profile of dark matter remains approximately flat) is constant across a wide range of galaxies1. This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence1,2,3. Here we report that the luminous matter surface density is also constant within one scale-length of the dark halo. This means that the gravitational acceleration generated by the luminous component in galaxies is always the same at this radius. Although the total luminous-to-dark matter ratio is not constant, within one halo scale-length it is constant. Our finding can be interpreted as a close correlation between the enclosed surface densities of luminous and dark matter in galaxies4.

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Figure 1: Universality of the average surface density (and gravity) of baryons within the halo core radius.


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G.G. was supported by the FWO-Vlaanderen (Belgium), and B.F. was supported in part by the Alexander von Humboldt foundation (Germany), the FNRS (Belgium), and the CNRS (France). We thank A. Jorissen and L. Hill for their comments on the manuscript.

Author Contributions G.G. and B.F. contributed to analysing and interpreting the data, making the figures, and writing the paper. HS.Z. and P.S. contributed to interpreting the data.

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Correspondence to Gianfranco Gentile.

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This file contains Supplementary Notes and Data, Supplementary References, Supplementary Table 1and Supplementary Figures 1-3 with References. (PDF 198 kb)

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Gentile, G., Famaey, B., Zhao, H. et al. Universality of galactic surface densities within one dark halo scale-length. Nature 461, 627–628 (2009).

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