Global stability of self-gravitating discs in modified gravity

Abstract

We study the global stability of a self-gravitating disc in the context of Modified Gravity (MOG) using N-body simulations. This theory is a relativistic scalar-tensorvector theory of gravity and presented to address the dark matter problem. In the weak field limit MOG possesses two free parameters α and µ 0 which have been already determined using rotation curve data of spiral galaxies. The evolution of a stellar selfgravitating disc and more specifically the bar instability in MOG is investigated and compared to a Newtonian case. Our models have exponential and Mestel-like surface densities as Σ ∝ exp(−r/h) and Σ ∝ 1/r. It is found out that, surprisingly, the discs are more stable against the bar mode in MOG than in Newtonian gravity. In other words, the bar growth rate is effectively slower than the Newtonian discs. Also we show that both free parameters, i.e. α and µ 0 , have stabilising effects. In other words, increase in these parameters will decrease the bar growth rate.

Stellar Bar Evolution in the Absence of Dark Matter Halo

“…In the bottom panel this will happen at larger times. This fact has also been reported in Ghafourian & Roshan (2017). The bar pattern speed has been shown in Fig.…”

“…In fact, the procedure in Ghafourian & Roshan (2017) is similar to what presented in Ostriker & Peebles (1973), in which it has been proved that a rigid halo has stabilizing effects. The maximum number of particles in Ghafourian & Roshan (2017) is 2 × 10 4 . Therefore the results may suffer from numeric artifacts caused by employing small number of particles.…”

“…Therefore we have to enlarge the grid in order to avoid particles to escape from the grid. In the following let us briefly show that the main results of Ghafourian & Roshan (2017) do not change by increasing the number of particles. Then we will discuss more realistic models by adding dark matter halos to the Newtonian models.…”

“…Roshan et al (2016) investigated the global stability of the Maclaurin disk in MOG using semi analytic method. On the other hand the global stability of exponential and Mestel disk galaxies in MOG has been investigated in Ghafourian & Roshan (2017) using a low resolution N-body simulations. Although there is no meaningful difference in the local stability of disk galaxies in MOG and the dark matter model, the global stability is substantially different.…”

Local stability of galactic discs in modified dynamics

“…For example, Milgrom (1989) investigates local stabilities of discs governed by MOND dynamics, Roshan & Abbassi (2014, 2015a) study the effects of MOG while the implications of f (R) have been surveyed by Roshan & Abbassi (2015b). Also Roshan et al (2016) and Ghafourian & Roshan (2017) study the global stability of galactic discs under MOG from theoretical and numerical point of view respectively.…”