Trying to explain the result described in the paper below in the LambdaCDM paradigm with tidal stripping of dark matter is really a stretch. If the dark matter particles are stripped, where do they go? Why is dark matter differentially stripped relative to regular matter? And, why is this observation only being explained in retrospect, rather than predicted in advance?
But, in the MOND paradigm, the transition of a galaxy from a more extended and dispersed spiral form to a more compact lenticular galaxy automatically and naturally results in weak inferred dark matter phenomena. This observation was expected back in 1983 when it was first formulated. This is because, in the MOND paradigm, lenticular galaxies are expected to have less inferred dark matter phenomena than spiral galaxies, because more of their matter is within the critical MOND acceleration region.
We present the high-sensitivity and large-scale atomic hydrogen (HI) observations towards lenticular (S0) galaxy NGC 4111 using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). The column density map shows that NGC4111 and seven other different types of galaxies share a huge HI gas complex. The data also suggest that NGC 4111 is interacting with seven galaxies. Moreover, we identified a rotating gas disk associated with NGC 4111 from the HI complex. Still, the HI disk rotation direction has deviated from its stellar disk about 34.2∘, indicating that the NGC 4111 galaxy is undergoing a transition from a spiral galaxy to an S0 galaxy by the tidal interactions.
The obtained dark matter-to-stellar mass ratio of NGC4111 is 3.1±0.7, which is lower than the average value of the Local Universe, implying that the interactions may strip its dark matter. Our results suggest that in a galaxy group environment, tidal interactions have a significant effect on galaxy features.
Mei Ai, et al., "Formation of the dark-matter deficient S0 galaxy NGC 4111 under the tidal interactions" arXiv:2503.05171 (March 7, 2025).
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arXiv:2503.07106 (gr-qc)
[Submitted on 10 Mar 2025]
Is MOND necessarily nonlinear?
Mordehai Milgrom
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The iconic, deep-MOND-limit (DML) relation between acceleration and mass, a∼(MA0)1/2/r, implies that, in MOND, accelerations cannot be linear in the mass distribution (A0≡Ga0 is the DML constant, and a0 the MOND acceleration). This leads to important idiosyncracies of MOND, such as a breakdown of the strong equivalence principle, and the resulting ``external-field effect''. I show that the DML axioms are, in themselves, consistent with a, possibly unique, nonrelativistic, action-based, linear formulation of the DML. This model suffers from important drawbacks, which may make it unacceptable as a basis for a full-fledged MOND theory. The model is unique among MOND theories propounded to date not only in being linear -- hence not exhibiting an external-field effect, for example -- but in constituting a modification of both Newtonian inertia and Newtonian gravity. This linear and time-local model inspires and begets several, one-parameter families of models. One family employs nonlinear, time-nonlocal kinetic terms, but still linear gravitational-field equations. Other families generalize the DMLs of AQUAL and QUMOND, modifying gravity as well as inertia. All families employ fractional time derivatives and possibly fractional Laplacians. At present, I cannot base some acceptable MOND theory on these models -- for example, I cannot offer a sensible umbrella theory that interpolates between these DML models and Newtonian dynamics. They are, however, quite useful in elucidating various matter-of-principle aspects of MOND; e.g., they help to understand which predictions follow from only the basic tenets of MOND -- so-called primary predictions -- and which are secondary, i.e., theory dependent. The models may also show the way to a wider class of MOND theories. (Abridged.)
Comments: 21 pages
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Phenomenology (hep-ph)
Cite as: arXiv:2503.07106 [gr-qc]
Good catch. Thanks for the heads up.
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