The dynamics of the bulge dominated galaxy NGC 7814 in MOND

Context. The bulge dominated galaxy NGC 7814 provides one of the strongest dynamical tests possible for MOdified Newtonian Dynamics (MOND). Spitzer 3.6 μm photometry fixes the bulge parameterisation and strongly constrains the properties of the subdominant stellar disk. Furthermore, the distance is known to better than 5%, virtually eliminating it as a free parameter. The rotation curve is easily measured, since the H I (and stellar) disks are edge on, and both the receding and approaching sides agree very well. Aims. We explore the agreement between the model and observed rotation curves in MOND given that the only two free parameters available are the mass-to-light ratios of the bulge and disk. Methods. We use a grid based MOND Poisson solver that accurately solves for the MOND gravity and produces our model rotation curves from a given mass distribtion. The input to the Poisson solver is a 3D distribution of N particles which is generated from modelling the observed distribution of stars and gas in the galaxy. Results. By ensuring a superior fit to the radial surface brightness profile than previous works, by virtue of a double Sérsic fit to the bulge, we were able to produce excellent fits to the rotation curve with typical values for both mass-to-light ratios. Conclusions. The model rotation curve of a mass distribution in MOND is extremely sensitive to the bulge-disk decomposition and even slight deviation from the observed mass distribution can produce large differences in the model rotation curve.