ΛCDM with baryons versus MOND: The time evolution of the universal acceleration scale in the Magneticum simulations

Abstract

ABSTRACT MOdified Newtonian Dynamics (MOND) is an alternative to the standard Cold Dark Matter (CDM) paradigm which proposes an alteration of Newton’s laws of motion at low accelerations, characterized by a universal acceleration scale a0. It attempts to explain observations of galactic rotation curves and predicts a specific scaling relation of the baryonic and total acceleration in galaxies, referred to as the Rotational Acceleration Relation (RAR), which can be equivalently formulated as a Mass Discrepancy Acceleration Relation (MDAR). The appearance of these relations in observational data such as SPARC has lead to investigations into the existence of similar relations in cosmological simulations using the standard ΛCDM model. Here, we report the existence of an RAR and MDAR similar to that predicted by MOND in ΛCDM using a large sample of galaxies extracted from a cosmological, hydrodynamical simulation (Magneticum). Furthermore, by using galaxies in Magneticum at different redshifts, a prediction for the evolution of the inferred acceleration parameter a0 with cosmic time is derived by fitting a MOND force law to these galaxies. In Magneticum, the best fit for a0 is found to increase by a factor ≃3 from redshift z = 0 to z = 2.3. This offers a powerful test from cosmological simulations to distinguish between MOND and ΛCDM observationally.