Dynamics of DiskMass Survey galaxies in refracted gravity

Abstract

We test if Refracted Gravity (RG) can describe the dynamics of disk galaxies without resorting to the presence of dark matter. RG is a classical theory of gravity where the standard Poisson equation is modified with the introduction of the gravitational permittivity, a universal monotonic function of the local mass density. We use the rotation curves and the radial profiles of the stellar velocity dispersion perpendicular to the galactic disks of 30 disk galaxies from the DiskMass Survey (DMS) to determine the gravitational permittivity. RG describes the rotation curves and the vertical velocity dispersions by requiring galaxy mass-to-light ratios in agreement with stellar population synthesis models, and disk thicknesses in agreement with observations, once observational biases are taken into account. Our results rely on setting the three free parameters of the gravitational permittivity for each individual galaxy. However, we show that the differences of these parameters from galaxy to galaxy can in principle be ascribed to statistical fluctuations. We adopt an approximate procedure to estimate a single set of parameters that might properly describe the kinematics of the entire sample and suggest that the gravitational permittivity is indeed a universal function. We finally show that the RG models of the individual rotation curves can only partly describe the radial acceleration relation (RAR), between the observed centripetal acceleration derived from the rotation curve and the Newtonian gravitational acceleration originating from the baryonic mass distribution. Evidently, the RG models underestimate the observed accelerations by 0.1 to 0.3 dex at low Newtonian accelerations. An additional serious problem is the strong correlations, at largely more than 5σ, between the residuals of the RAR models and three radially-dependent properties of the galaxies, whereas the DMS data show considerably less significant correlations, at more than 4σ, for only two of these quantities. These correlations might originate the non-null intrinsic scatter of the RG models, at odds with the observed intrinsic scatter of galaxy samples, different from DMS, which is consistent with zero. Further investigations are required to assess if these discrepancies in the RAR originate from the DMS sample, which might not be ideal for deriving the RAR, or if they are genuine failures of RG.

Dark Matters on the Scale of Galaxies

“…Similarly, we can see the appearance of a 0 in the RAR, between the observed centripetal acceleration derived from the rotation curve of disk galaxies and the Newtonian gravitational acceleration generated by the baryonic mass distribution (Figure 4): the deviation from the one-to-one relation appears at Newtonian accelerations smaller than a 0 and the relation is described by the interpolation function of Equation (19) [127]. Although the agreement shows no scatter and no dependence of the residuals on the galaxy properties [128,129], as expected for a relation driven by gravity alone, additional investigations are required to confirm these results, because some dependence of the residuals on the galaxy properties appears to be present in other galaxy samples different from SPARC [151,152].…”

“…An additional unsettled controversy is the correlation between the residuals of the observed rotation curves from relation (4) and the properties of the galaxies observed in galaxy samples [151,152] different from SPARC, where this correlation appears to be absent [130].…”

Dynamics of Disk and Elliptical Galaxies in Refracted Gravity

“…The results of this work are collected in [2]. We model the rotation curves and the vertical velocity dispersions perpendicular to the galaxy disks from the mass distributions of 30 disk galaxies in the DMS.…”

“…We investigate the dynamics of disk and elliptical galaxies with Refracted Gravity (RG) [1,2], a novel classical theory of modified gravity inspired to electrodynamics in matter, which does not resort to dark matter. The presence of dark matter is instead mimicked by a gravitational permittivity, ( ), a monotonic increasing function of the local mass density, , which depends on three universal parameters.…”

“…Specifically, the larger the value of the steeper the transition (see Fig. 1 of [2]). Summarizing, RG has three free parameters, , and , supposed to be universal.…”