MOND and Isolated Elliptical Galaxies—NGC 6411

NGC 6411, an isolated elliptical galaxy, appears in the literature with an intermediate age of 3.5 Gyr. Its globular cluster system (GCS), on the other hand, has all the properties of a very old age. The knowledge of the stellar M/L ratio is necessary to evaluate its mass discrepancy. NGC 6411 has a low central surface brightness, which makes it a valuable test object for Modified Newtonian Dynamics (MOND). We reconsider the conflict between age and GCS properties. We perform a stellar population analysis to constrain its baryonic mass and do a kinematical analysis to constrain the total mass. We use data cubes from the CALIFA (Calar Alto Legacy Integral Field Area) survey to investigate the stellar population and measure velocity dispersions of NGC 6411, employing the spectral synthesis codes Starlight and ppxf. The dynamical analysis is based on spherical Jeans models. Using Starlight, an intermediate age of NGC 6411 results only as a Single Stellar Population (SSP) age with a fixed reddening. This seems to be caused by a slightly erroneous continuum slope. ppxf, which does not fit the continuum, gives an SSP age of 12 Gyr. A simple isotropic MOND model reproduces the projected velocity dispersions well. NGC 6411 joins the list of early-type galaxies for which MOND makes a successful prediction. It is special in the sense that due to its low surface brightness, MOND effects become visible at smaller radii than in other elliptical galaxies.