| Description: | Today's colloquium will be about a number of observational projects aimed at better understanding the existence and nature of dark matter, and also aimed at testing alternatives to galactic dark matter such as MOND (Modified Newtonian Dynamics). A remarkable property of dark matter halos in galaxies will be discussed: when fitted with a dark-matter halo with a constant density core, galaxy kinematics and weak lensing data reveal a constant dark matter surface density of about 110 Msol/pc**2, for objects spanning 14 galaxy magnitudes. Predictions of different models for the Radial Tully-Fisher relation (RTF), a series of Tully-Fisher-like relations measured at different radii will also be discussed. The talk will also be about tidal dwarf galaxies, which within the CDM framework are expected to be dark matter-free but instead have a mass discrepancy, of the magnitude that is expected in MOND.
The image shows the average central surface density of cored dark matter halos vs. magnitude. This is done for a wide range of objects spanning 14 magnitudes and the entire Hubble sequence. The dark matter parameters (central density and core radius) were estimated in various independent ways. Despite the huge range in luminosities, the average surface density is approximately constant at about 110+50-30 Msol/pc**2, when the dark matter halo was assumed to have a central constant density core. Different symbols represent different objects. From Donato et al., submitted. |
