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

TL;DR

This paper investigates the distribution of phantom dark matter predicted by Milgromian gravity (MOND) in the Local Universe, comparing it with dark matter models, and explores implications for galaxy dynamics and weak lensing.

Contribution

It introduces a detailed analysis of the phantom dark matter distribution in QUMOND, including the SHMR, external field effects, and weak lensing predictions, providing new insights into MOND's local predictions.

Findings

The stellar-to-phantom-halo-mass relation follows a power-law similar to observations.

The gas-to-phantom-halo-mass relation is flat across the Local Volume.

Negative phantom dark matter density zones are predicted around galaxies.

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, $\Omega_{\rm pdm} \approx 0.1$, below the average cold dark matter density in a $\Lambda$CDM 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 $z \sim 0.3$.