A better understanding of the formation of mass structures in the universe can be obtained by determining the amount and distribution of dark and luminous matter in spiral galaxies. To investigate such matters a sample of 12 galaxies, most with accurate distances, has been composed of which the luminosities are distributed regularly over a range spanning 2 1 2 orders of magnitude. Of the observed high quality and extended rotation curves of these galaxies decompositions have been made, for four different schemes, each with two free parameters. For a "maximum disc fit" the rotation curves can be well matched, yet a large range of mass-to-light ratios for the individual galaxies is required. For the alternative gravitational theory of MOND the rotation curves can be explained if the fundamental parameter associated with MOND is allowed as a free parameter. Fixing that parameter leads to a disagreement between the predicted and observed rotation curves for a few galaxies. When cosmologically motivated NFW dark matter halos are assumed, the rotation curves for the least massive galaxies can, by no means, be reproduced; cores are definitively preferred over cusps. Finally, decompositions have been made for a pseudo isothermal halo combined with a universal M/L ratio. For the latter, the light of each galactic disc and bulge has been corrected for extinction and has been scaled by the effect of stellar population. This scheme can successfully explain the observed rotations and leads to sub maximum disc mass contributions. Properties of the resulting dark matter halos are described and a ratio between dark and baryonic mass of ∼ 9 for the least, and of ∼ 5, for the most luminous galaxies has been determined, at the outermost measured rotation.

We present an efficient technique for calculating the midplane gravitational potential of a thin axisymmetric galactic disk. The applicable gravitational theory may be Newtonian or non-Newtonian. By taking into account the disk's vertical structure, there is no Green's function singularity in the solution integration. Our derivations are relatively simple, but we stop at a level where Mathematica can easily take over and execute what otherwise would be tedious and uninformative mathematical manipulations.

We show some significance against the null hypothesis of random interactions of binary spiral galaxies, and in favour of the alternative that more interactions than expected occur for axes either nearly parallel (spins being parallel or anti‐parallel) or nearly orthogonal. We discuss this in the context of similar prior studies, using a different statistical focus in such a way that we are able to incorporate additional data.

The van Dam-Veltman-Zakharov (vDVZ) discontinuity requires that the mass m of the graviton is exactly zero, otherwise measurements of the deflection of starlight by the Sun and the precession of Mercury's perihelion would conflict with their theoretical values. This theoretical discontinuity is open to question for numerous reasons. In this paper we show from a phenomenological viewpoint that the m > 0 hypothesis is in accord with Supernova Ia and CMB observations, and that the large scale structure of the universe suggests that m ∼ 10 −30 eV/c 2 .

Certain covariant theories of the modified Newtonian dynamics paradigm seem to require an additional hot dark matter (HDM) component -in the form of either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs) with a mass around 11eV -to be relieved of problems ranging from cosmological scales down to intermediate ones relevant for galaxy clusters. Here we suggest using gravitational lensing by galaxy clusters to test such a marriage of neutrino HDM and modified gravity, adopting the framework of tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter (CDM), such HDM is subject to strong phase-space constraints, which allows one to check cluster lens models inferred within the modified framework for consistency. Since the considered HDM particles cannot collapse into arbitrarily dense clumps and only form structures well above the galactic scale, systems which indicate the need for dark substructure are of particular interest. As a first example, we study the cluster lens Abell 2390 and its impressive straight arc with the help of numerical simulations. Based on our results, we outline a general and systematic approach to model cluster lenses in TeVeS which significantly reduces the calculation complexity. We further consider a simple bimodal lens configuration, capable of producing the straight arc, to demonstrate our approach. We find that such a model is marginally consistent with the hypothesis of 11eV SNs. Future work including more detailed and realistic lens models may further constrain the necessary SN distribution and help to conclusively assess this point. Cluster lenses could therefore provide an interesting discriminator between CDM and such modified gravity scenarios supplemented by SNs or other choices of HDM.