The mass distribution in Spiral galaxies

In the past years a wealth of observations has allowed us to unravel the structural properties of the Dark and Luminous mass distribution in spirals. As result, it has been found that their rotation curves follow, out their virial radius, an Universal function (URC) made by two terms: one due to the gravitational potential of a Freeman stellar disk and the other due to that of a dark halo. The importance of the latter is found to decrease with galaxy mass. Individual objects reveal in detail that dark halos have a density core, whose size correlates with its central value. These properties will guide $\Lambda$CDM Cosmology to evolve to match the challenge that observations presently pose.Comment: 10 pages, Invited review for IAU Symposium 244, Dark Galaxies & Lost Baryons. Typos corrected. Comments are welcom

Universal properties in galaxies and cored Dark Matter profiles

In this paper I report the highlights of the talk: "Universal properties in galaxies and cored Dark Matter profiles", given at: Colloquium Lectures, Ecole Internationale d'Astrophysique Daniel Chalonge. The 14th Paris Cosmology Colloquium 2010 "The Standard Model of the Universe: Theory and Observations"

The Baryonic Mass Function of Spiral Galaxies: Clues to Galaxy Formation

We compute the baryonic mass function (BMF) of disc galaxies using the best LFs and baryonic M/L ratios reliable for this goal. For baryonic masses (M_b) ranging between 10^8 and 10^{11} solar masses, the BMF is featureless, i.e. it scales as M_b^{-1/2}. Outside this mass range, the BMF is a strong inverse function of M_b. The contributions to the baryon density Omega_b from objects of different mass highlight a characteristic mass scale of spirals at about 2x10^{11} solar masses, around which >50% of the total baryonic mass is concentrated. The integral value, Omega_b= 1.4x10^{-3}, confirms, to a higher accuracy, previous evidence (Persic & Salucci 1992) that the fraction of BBN baryons locked in disc galaxies is negligible and matches that of high-z Damped Lyman Alpha systems (DLAs). We investigate the scenario where DLAs are the progenitors of present-day spirals, and find a simple relationship between their masses and HI column densities by which the DLA mass function closely matches the spiral BMF.Comment: MNRAS, in press. Replaces previous, unrefereed version. 10 pages MNRAS style LaTeX, 7 figure

The Dark Matter Distribution in Disk Galaxies

We use high-quality optical rotation curves of 9 low-luminosity disk galaxies to obtain the velocity profile of the surrounding dark matter halos. We find that they increase linearly with radius at least out to the stellar disk edge, implying that, over the entire region where the stars reside, the density of the dark halo is constant. The properties of the halo mass structure found are similar to that claimed for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in standard cold dark matter scenario and those actually detected around galaxies. We find that the density profile proposed by Burkert (1995) reproduces the halo rotation curves, with halo central densities and core radii scaling as $\rho_0 \propto r_0^{-2/3}$.Comment: 8 pages, 6 figures, MNRAS accepted. New section and figures added, concerning CDM mass models. Minor changes to the rest of the pape

Dark Matter and MOOCs

To teach the topic of Dark Matter in Galaxies to undergraduate and PhD students is not easy, one reason being that the scientific community has not converged yet to a generally shared knowledge. We argue that the teaching of this topic and its subsequent scientific progress may benefit by Massive Online and Open Courses. The reader of this paper can express his/her opinion on this by means of a confidence vote at: https://moocfellowship.org/submissions/dark-matter-in-galaxies-the-last-mysteryComment: 2 Pages, Coments Welcom

Testing MOND with Local Group spiral galaxies

The rotation curves and the relative mass distributions of the two nearby Local Group spiral galaxies, M31 and M33, show discrepancies with Modified Newtonian dynamic (MOND) predictions. In M33 the discrepancy lies in the kinematics of the outermost regions. It can be alleviated by adopting tilted ring models compatible with the 21-cm datacube but different from the one that best fits the data. In M31 MOND fails to fit the falling part of the rotation curve at intermediate radii, before the curve flattens out in the outermost regions. Newtonian dynamics in a framework of a stellar disc embedded in a dark halo can explain the complex rotation curve profiles of these two galaxies, while MOND has some difficulties. However, given the present uncertainties in the kinematics of these nearby galaxies, we cannot address the success or failure of MOND theory in a definite way. More sensitive and extended observations around the critical regions, suggested by MOND fits discussed in this paper, may lead to a definite conclusion.Comment: 6 pages, 4 figures. To be published in MNRA

The Extended Rotation Curve and the Dark Matter Halo of M33

We present the 21-cm rotation curve of the nearby galaxy M33 out to a galactocentric distance of 16 kpc (13 disk scale-lengths). The rotation curve keeps rising out to the last measured point and implies a dark halo mass larger than 5 10^{10} solar masses. The stellar and gaseous disks provide virtually equal contributions to the galaxy gravitational potential at large galactocentric radii but no obvious correlation is found between the radial distribution of dark matter and the distribution of stars or gas. Results of the best fit to the mass distribution in M33 picture a dark halo which controls the gravitational potential from 3 kpc outward, with a matter density which decreases radially as R^{-1.3}. The density profile is consistent with the theoretical predictions for structure formation in hierarchical clustering cold dark matter models but mass concentrations are lower than those expected in the standard cosmogony.Comment: 11 pages, 10 figures, MNRAS latex style, accepted by MNRA

Cold Dark Matter Halos Must Burn

High-quality optical rotation curves for a sample of low-luminosity spirals evidence that the dark halos around galaxies are inconsistent with the output of proper CDM simulations. In fact, dark halos enveloping stellar disks are structures with approximately a constant density out to the optical edges. This is in strong disagreement with the characteristic rho(r) ~ r^(-1.5) CDM regime and severely challenges the "standard" CDM theory, also because the halo density appears to be heated up, at gross variance with the hierarchical evolution of collision-free particles.Comment: 2 figures, definitive version to appear in the Proceedings of the MPA/ESO/MPE/USM Joint Conference: "Lighthouses of the Universe: The Most Luminous Celestial Objects and their use for Cosmology", August 2001, Garching, German