Spiral Galaxy Mass Models:

MOND Models

The following is the abstract for a paper in production entitled `MOND Mass Models of Spiral Galaxies'.

Using two-dimensional velocity maps and I-band photometry, we have created modified Newtonian dynamics (MOND) mass models of 40 spiral galaxies, complementing previous work. The mass-to-light ratio parameters of the models are presented along with a discussion of the correlation between these values and the galaxies' colors. We also demonstrate this correlation for a subsample of Hydra cluster galaxies. Using a Bayesian comparison technique, we derive quantitative relations between MOND, Newtonian stars-only, and several different dark matter halo models to determine which type of model is most successful in describing the data. While we have not explored an exhaustive set of models, we believe they represent a fair cross section of likely possibilities. We also note that common systematic uncertainties typical of these galaxies can render such statistical comparisons inappropriate. We further discuss the details of two galaxies which provide preliminary evidence against MOND and investigate the impact of relaxing the assumption of constant mass-to-light ratios in these cases. We conclude that; 1) in a "chi-by-eye" sense, MOND mass models can fit spiral galaxy velocity maps as well as dark matter halo models, 2) unlike dark matter halo models of these galaxies, MOND models produce a trend between mass-to-light ratios and galaxy color, 3) in a strict statistical sense, fixed-distance, spatially constant mass-to-light ratio MOND mass models generally do not describe spiral galaxy velocity fields as economically as do some dark matter halo models, 4) one must be very careful when interpreting such a statement, as systematic effects in distance estimates, gas content, and mass-to-light gradients can strongly impact MOND fits.

The PDF draft version of this paper is available here