1. Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B-9000 Gent, Belgium
2. Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, Bvd du Triomphe, B-1050, Bruxelles, Belgium
3. CNRS UMR 7550, Observatoire Astronomique, Université de Strasbourg, F-67000 Strasbourg, France
4. AIfA, Universität Bonn, D-53121 Bonn, Germany
5. SUPA, School of Physics and Astronomy, University of St Andrews, KY16 9SS, UK
6. Leiden University, Sterrewacht and Instituut-Lorentz, Niels-Bohrweg 2, 2333 CA, Leiden, the Netherlands
7. SISSA International School for Advanced Studies, via Beirut 4, I-34151, Trieste, Italy

Correspondence to: Gianfranco Gentile^1,2 Correspondence and requests for materials should be addressed to G.G. (Email: gianfranco.gentile@ugent.be).

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 sequence^{1, 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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