The DAMAE project aims at measuring the relative content of DM in the haloes of elliptical galaxies of various luminosities. Measuring the mass distribution in early-type galaxies at radial distances comparable to those of the HI disks in spirals is instead much more troublesome just for the lack of easy tracers. The first, sparse and uncertain evidences of the presence of DM in ellipticals arose only at the end of the 80s. They rested mostly on X-ray emission from hot gas haloes wrapping some galaxies (however limited to the most massive objects, located at the centres of groups and clusters) and the HI emission from the rare gaseous disks around peculiar ellipticals. In the 90s, gravitational lensing (GL) came out as a promising astrophysical tool to investigate the mass distribution in ellipticals, with an ever growing sample of lensing galaxies. While this tool is extremely effective in constraining the mass distribution, it only allows one to study relatively distant objects (z > 0.1), poorly spatially resolved, and at an evolutionary stage different from the nearby galaxies, which represent our reference sample. Our team has a long-term expertise in the field of gravitational lensing galaxies (and galaxy clusters), in particular using novel observational techniques such as the integral-field spectroscopy.
However, X-ray emissions and GL do not provide any information about the motion of stars - the main constituents of early-type galaxies, which keep in the distribution of their orbit the record of the evolutionary path of the host galaxy. In order to gain insight into early-type galaxies, it is therefore mandatory to understand how stars behave. Studying stellar motions at distances where DM is predicted to dominate (R > 2-3Reff, Reff being the so-called effective radius, including half of the galaxy light) is now possible with a systematic use of planetary nebulae (PNe). Their observations are combined with a sophisticated modelling and analysis relying upon the high number of these "test particles", and with the tools optimized for their discovery and radial velocity measurements. Members of the Research Team are co-Is of the only instrument so far available for such observations, the Planetary Nebula Spectrograph (PN.S), currently mounted at the 4-m W.Herschel telescope, at the observatory of El Roque de los Muchachos, La Palma, Spain.
With the present project we aim at making significant steps in the study of the mass distribution in elliptical galaxies. The ongoing observational programs involving the DAMAE Team will allow, together with existing literature/public data, to enlarge the galaxy sample with reliable mass distribution done.
In particular we aim at completing the study of a dozen of elliptical galaxies, within the PN.S collaboration. For some of these systems, we have carried on observational programs at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) have provided further stellar kinematics data (this time within Re) of the galaxies already in the PN.S sample either via long slit spectroscopy (March 2008) or integral field spectroscopy (April and October 2007).
This wealth of data, homogeneously organized, will then represent an unprecedented base to address some fundamental questions about DM and its role in galaxy formation. In particular we aim at contributing to the clarification of the following questions:
1) Does the mass density distribution in elliptical galaxies follow a NFW profile with concentration and virial mass consistent with the results from cosmological simulations, at every cosmic epoch and in any mass range?
2) Do different models based upon cosmological simulations - isothermal or cored profiles - give a better description of galaxy kinematics, or is it necessary to consider mass models within the framework of alternative gravity theories?
3) Are discrepancies with respect to the LCDM model correlated with the galaxies global properties (i.e. morphology, internal distribution of the orbits, angular momentum, total luminosity, central BH mass), thus pointing to some effect of the baryonic physics on the final DM distribution?
4) Is the relationship of the ratio (luminous mass)/(dark mass) with the luminous mass (and redshift) similar in ellipticals and spirals? The answer to this question is essential in order to understand whether the star formation efficiency is a function of the galaxy mass only (as suggested by cosmological simulations) or of other physical quantities also, as the angular momentum (which is the main property to discriminate between spirals and ellipticals).
5) Are Extended Theories of Gravity, in particular the so-called F(R) a more realistic alternative to the dark matter which is raised in the Newtonian framework?
