SIMBAD references

Prompted by the recent claim, by Donato et al., of a quasi-universal central surface density of galaxy dark matter haloes, I look at what MOND has to say on the subject. MOND, indeed, predicts a quasi-universal value of this quantity for objects of all masses and of any internal structure, provided they are mostly in the Newtonian regime; i.e. their mean acceleration is at or above a₀. The predicted value is γΣ_M, with Σ_M≡ a₀/2πG = 138(a₀/1.2 x10^–8cm/s2)M_☉/pc2 and γ is a constant of the order of 1 that depends only on the form of the MOND interpolating function. For the nominal value of a₀, log(Σ_M/M_☉/pc2) = 2.14, which is consistent with that found by Doanato et al. of 2.15±0.2.

MOND predicts, on the other hand, that this quasi-universal value is not shared by objects with much lower mean accelerations. It permits halo central surface densities that are arbitrarily small, if the mean acceleration inside the object is small enough. However, for such low-surface-density objects, MOND predicts a halo surface density that scales as the square root of the baryonic one, and so the range of the former is much compressed relative to the latter. This explains, in part, the finding of Donato et al. that the universal value applies to low-acceleration systems as well. Looking at literature results for a number of the lowest surface density disc galaxies with rotation curve analysis, I find that, indeed, their halo surface densities are systematically lower then the above `universal' value.

The prediction of Σ_M_ as an upper limit, and accumulation value, of halo central surface densities pertains, unlike most other MOND predictions, to a pure `halo' property, not to a relation between baryonic and `dark matter' properties.