Abstract
The aim of this paper is to test the need for non-baryonic dark matter in the context of galactic rotation and the apparent difference between distributions of galactic mass and luminosity. We present a set of rotation curves and 3.6 μm surface brightness profiles for a diverse sample of 214 galaxies. Using rotation curves as the sole input into our Newtonian disk model, we compute non-parametric radial profiles of surface mass density. All profiles exhibit lower density than parametric models with dark halos and provide a superior fit with observed rotation curves. Assuming all dynamical mass is in main-sequence stars, we estimate radial distributions of characteristic star mass implied by the corresponding pairs of density and brightness profiles. We find that for 132 galaxies or 62% of the sample, the relation between density and brightness can be fully explained by a radially declining stellar mass gradient. Such idealized stellar population fitting can also largely address density and brightness distributions of the remaining 82 galaxies, but their periphery shows, on average, 14 M⊙/pc2 difference between total density and light-constrained stellar density. We discuss how this density gap can be interpreted, by considering a low-luminosity baryonic matter, observational uncertainties, and visibility cutoffs for red dwarf populations. Lastly, we report tight correlation between radial density and brightness trends, and the discovered flattening of surface brightness profiles—both being evidence against dark matter. Our findings make non-baryonic dark matter unnecessary in the context of galactic rotation.
Highlights
Elevated to the status of an axiomatic assumption, the concept of dark matter has settled firmly in modern astrophysics and cosmology
For each galaxy in our sample, as well as for sample-level “average galaxy”, we study the radial profiles of the two above-defined metrics, characteristic star mass and excess density
For galaxies where characteristic star mass always stays above the minimal star mass limit, we conclude that no dark matter is required at all within the density/brightness observational radii to explain empirical observations of rotation and luminosity
Summary
Elevated to the status of an axiomatic assumption, the concept of dark matter has settled firmly in modern astrophysics and cosmology. Has empirical evidence of anomalous phenomena been established beyond a reasonable doubt, backed by a wealth of strong data and realistic assumptions? What if dark matter is regular baryons obscured by observational limitations and analytical habits? Our focus here is on the apparent difference between expected mass distribution and luminosity in galaxies, which is one of the main reasons for the dark matter hypothesis. It has been widely reported that in most galaxies, light intensity declines faster than mass density away from the center [11,12,13,14]. We use the term “density” to refer to “surface mass density”, for brevity
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