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

Understand

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 galaxies.

• This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence.
• 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.