The phantom dark matter halos of the Local Volume in the context of modified Newtonian dynamics

Abstract

We explore the predictions of Milgromian gravity (MOND) in the Local Universe by considering the distribution of the 'phantom' dark matter (PDM) that would source the MOND gravitational field in Newtonian gravity, allowing an easy comparison with the dark matter framework. For this, we specifically deal with the quasi-linear version of MOND (QUMOND). We compute the 'stellar-to-(phantom)halo-mass relation' (SHMR), a monotonically increasing power-law resembling the SHMR observationally deduced from spiral galaxy rotation curves in the Newtonian context. We show that the gas-to-(phantom)halo-mass relation is flat. We generate a map of the Local Volume in QUMOND, highlighting the important influence of distant galaxy clusters, in particular Virgo. This allows us to explore the scatter of the SHMR and the average density of PDM around galaxies in the Local Volume, Ω pdm ≈ 0.1, below the average cold dark matter density in a ΛCDM Universe. We provide a model of the Milky Way in its external field in the MOND context, which we compare to an observational estimate of the escape velocity curve. Finally, we highlight the peculiar features related to the external field effect in the form of negative PDM density zones in the outskirts of each galaxy, and test a new analytic formula for computing galaxy rotation curves in the presence of an external field in QUMOND. While we show that the negative PDM density zones would be difficult to detect dynamically, we quantify the weak lensing signal they could produce for lenses at z ∼ 0.3.

Numerical Solutions of the External Field Effect on the Radial Acceleration in Disk Galaxies

“…Our results are also compared with literature numerical or approximate results. The QUMOND results match recent simulation results (Zonoozi et al 2021;Oria et al 2021). However, the AQUAL results show differences from previously published simulation or approximate results Haghi et al 2019).…”

“…where y = (g N /a 0 ) 2 + e 2 N . Note that the function proposed by Oria et al (2021) is similar to this function but deviates in the asymptotic limit.…”

“…Our numerical results match accurately the corresponding analytic asymptotic limits of AQUAL and QUMOND (Equations ( 4) and ( 5)). Note that published N-body based numerical simulation results in AQUAL (Haghi et al 2019) or QUMOND (Oria et al 2021) do not match the asymptotic limits precisely probably due to the limits of numerical precision.…”

“…This is a useful concept especially for comparing MOND predictions directly with dark matter inferences. For example, Oria et al (2021) have recently derived the phantom density distribution in the local volume using QUMOND.…”

“…Some more recent papers presented numerical results of the MOND EFE in disks (Zonoozi et al 2021) and in spherical systems (Oria et al 2021). These studies used the QUMOND formalism and considered the case that the external field is parallel to the rotation axis.…”