Garry W. Angus

Can MOND take a bullet? Analytical comparisons of three versions of MOND beyond spherical symmetry

A proper test of modified Newtonian dynamics (MOND) in systems of non-trivial geometries depends on modelling subtle differences in several versions of its postulated theories. This is especially true for lensing and dynamics of barely virialized galaxy clusters with typical gravity of scale a0. The original MOND formula, the classical single-field modification of the Poisson equation, and the multifield general relativistic theory of Bekenstein (tensor-vector-scalar, TeVeS) all lead to different predictions as we stray from spherical symmetry. In this paper, we study a class of analytical MONDian models for a system with a semi-Hernquist baryonic profile. After presenting the analytical distribution function of the baryons in spherical limits, we develop orbits and gravitational lensing of the models in non-spherical geometries. In particular, we can generate a multicentred baryonic system with a weak lensing signal resembling that of the merging galaxy cluster 1E 0657-56 with a bullet-like light distribution. We finally present analytical scale-free highly non-spherical models to show the subtle differences between the single-field classical MOND theory and the multifield TeVeS theory.

The collision velocity of the bullet cluster in conventional and modified dynamics

We consider the orbit of the bullet cluster 1E 0657−56 in both cold dark matter (CDM) and Modified Newtonian Dynamics (MOND) using accurate mass models appropriate to each case in order to ascertain the maximum plausible collision velocity. Impact velocities consistent with the shock velocity (∼ 4700 km s −1 ) occur naturally in MOND. CDM can generate collision velocities of at most ∼3800 km s −1 , and is only consistent with the data, provided that the shock velocity has been substantially enhanced by hydrodynamical effects.

X‐ray group and cluster mass profiles in MOND: unexplained mass on the group scale

Although very successful in explaining the observed conspiracy between the baryonic distribution and the gravitational field in spiral galaxies without resorting to dark matter (DM), the modified Newtonian dynamics (MOND) paradigm still requires DM in X-ray bright systems. Here, to get a handle on the distribution and importance of this DM, and thus on its possible form, we deconstruct the mass profiles of 26 X-ray emitting systems in MOND, with temperatures ranging from 0.5 to 9 keV. Initially, we compute the MOND dynamical mass as a function of radius, then subtract the known gas mass along with a component of galaxies which include the cD galaxy with M/L K = 1. Next, we test the compatibility of the required DM with ordinary massive neutrinos at the experimental limit of detection (m ν = 2 eV), with density given by the Tremaine-Gunn limit. Even by considering that the neutrino density stays constant and maximal within the central 100 or 150 kpc (which is the absolute upper limit of a possible neutrino contribution there), we show that these neutrinos can never account for the required DM within this region. The natural corollary of this finding is that, whereas clusters (T ≳ 3 keV) might have most of their mass accounted for if ordinary neutrinos have a 2 eV mass, groups (T ≲ 2 keV) cannot be explained by a 2 eV neutrino contribution. This means that, for instance, cluster baryonic dark matter (CBDM, Milgrom) or even sterile neutrinos would present a more satisfactory solution to the problem of missing mass in MOND X-ray emitting systems.

Is an 11 eV sterile neutrino consistent with clusters, the cosmic microwave background and modified Newtonian dynamics?

If a single sterile neutrino exists such that

Velocity dispersion around ellipticals in MOND

m_{\nu_s}\sim11eV

Tidal Disruption of the First Dark Microhalos

, it can serendipitously solve all outstanding issues of the Modified Newtonian Dynamics. With it one can explain the dark matter of galaxy clusters without influencing individual galaxies, match the angular power spectrum of the cosmic microwave background and potentially fit the matter power spectrum. This model is flat with

Current data on the globular cluster Palomar 14 are consistent with MOND (Research Note)

\Omega_{\nu_s}\sim0.23

The Modified Newtonian Dynamics Fundamental Plane

and the usual baryonic and dark energy components, thus the Universe has the same expansion history as the

Analysis of galactic tides and stars on CDM microhalos

\lcdm

Cold dark matter microhalo survival in the Milky Way

model and only differs at the galactic scale where the Modified Dynamics outperforms