Fig 1 - uploaded by Federico Re
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Ratio of the stellar to dark density in the ENS (top) and DM and stellar density profiles (bottom left and bottom right) in units of 3M/4πr 3 c for κ = 100 and γ = 0, 0.5, 1, 1.5, 2 and 2.5.
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Aims. We investigate the core-cusp problem of the Λ cold dark matter (ΛCDM) scenario in the context of the modified Newtonian dynamics (MOND) paradigm while exploiting the concept of an equivalent Newtonian system (ENS).
Methods. By means of particle-mesh N -body simulations in MOND, we explored the processes of galaxy formation via cold dissipatio...
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Context 1
... thus, even in the framework of (Qu)MOND the phantom DM halo does not really dominate in the central region for a cored stellar density profile. In Figure 1 we plot for γ = 0, 0.5, 1, 1.5, 2 and 2.5 the ratio of stellar to phantom DM and their respective radial density profiles for κ = 10 2 . We note that, remarkably, models with a strong cusp (i.e. ...
Context 2
... blue and green in the range 10 −3 ≤ 2K 0 /|W 0 | ≤ 0.5. Using Equation (8) for the angle-averaged final density profile on a spherical grid, we evaluated the density distribution of the DM component of the parent Newtonian model (see bottom panels, same figure). We find that, in qualitative agreement with the structural properties of the ENS (see Figs. 1 and 2 in Sect. 2), cuspy end systems can be associated with cored or weakly cuspy phantom halos. In general, the end products of spherical collapses have always inner regions that are baryon dominated when building their ENS, even if the initial conditions are such that κ = 1 (in particular for the γ = 0 ...
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In recent years, there has been an increase in the number of papers regarding general-relativistic explanations for the dark matter phenomena in disc galaxies. The main focus of this scientific discussion is whether a previously unexamined relativistic dragging vortex could support flat rotation curves, with various research groups taking different...
Citations
... In this paper, we have chosen the widely adopted form of interpolating function of Eqn. (21) as it has been proven to give a MOND realisation able to pass a variety of observational tests (Famaey & McGaugh 2012), and it is widely employed in the study of ingalaxy dynamics within the MOND scenario (see e.g., Re & Di Cintio 2023;Di Cintio et al. 2024). However, we caution that the results may change with different choices of the interpolating function, as already noted in previous SGL MOND studies (see, e.g., Sanders & Land 2008). ...
Disc galaxies represent a promising laboratory for the study of gravitational physics, including alternatives to dark matter, owing to the possibility of coupling rotation curves' dynamical data with strong gravitational lensing observations. In particular, Euclid, DES and LSST are predicted to observe hundreds of thousands of gravitational lenses. Here, we investigate disc galaxy strong gravitational lensing in the MOND framework. We employ the concept of equivalent Newtonian systems within the quasi-linear MOND formulation to make use of the standard lensing formalism. We derive the phantom dark matter distribution predicted for realistic disc galaxy models and study the impact of morphological and mass parameters on the expected lensing. We find purely MONDian effects dominate the lensing and generate non-trivial correlations between the lens parameters and the lensing cross section. Moreover, we show that the standard realisation of MOND predicts a number count of disc galaxy lenses of one order of magnitude higher than the dark matter-driven predictions, making it distinguishable from the latter in upcoming surveys. Finally, we show that disc galaxy gravitational lensing can be used to strongly constrain the interpolating function of MOND.
Aims. We explore the dynamical friction on a test mass in gravitational systems in the quasi-linear formulation of modified Newtonian dynamics (QuMOND).
Methods. Exploiting the quasi-linearity of QuMOND, we derived a simple expression for the dynamical friction in akin to its Newtonian counterpart in the standard Chandrasekhar derivation. Moreover, adopting a mean field approach based on the Liouville equation, we were able to obtain a more rigorous (albeit in integral form) dynamical friction formula that can be evaluated numerically for a given choice of the QuMOND interpolation function.
Results. We find that our results are consistent with those of previous works. We observe that the dynamical friction is stronger in MOND with respect to a baryon-only Newtonian system with the same mass distribution. This amounts to a correction of the Coulomb logarithmic factor via additional terms that are proportional to the MOND radius of the system. Moreover, with the aid of simple numerical experiments, we confirm our theoretical predictions and those of previous works based on MOND.
Context. Recent observational studies proposed an empirical relation between the dark-to-total mass ratio and ellipticity in elliptical galaxies based on their observed total dynamical mass-to-light ratio data M / L = (14.1 ± 5.4) ϵ . In other words, the larger the content of dark matter in the galaxy, the more the stellar component will be flattened. If true, this observation appears to be in stark contrast with the commonly accepted galaxy formation scenario, whereby this process takes place inside dark halos with reasonably spherical symmetry.
Aims. Comparing the processes of dissipationless galaxy formation in different theories of gravity and the emergence of the galaxy scaling relations therein provides an important framework within which, in principle, one can discriminate between these processes.
Methods. By means of collisionless N -body simulations in modified Newtonian dynamics (MOND) and Newtonian gravity with and without active dark matter halos, with both spherical and clumpy initial structure, I study the trends of intrinsic and projected ellipticities, Sérsic index, and anisotropy with the total dynamical-to-stellar mass ratio.
Results. I show that the end products of both cold spherical collapses and mergers of smaller clumps show an increasing departure from spherical symmetry for increasing values of the total dynamical-to-stellar mass ratio, at least in a range of halo masses. The equivalent Newtonian systems of the end products of MOND collapses show a similar behaviour. However, the M / L relation obtained from the numerical experiments in both gravities is rather different from that reported by Deur and coauthors.
