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

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 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

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

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

Analysis of Rotation Curves in the Framework of the Gravitational Suppression Model

We present an analysis of suitable rotation curves (RCs) of eight galaxies, aimed at checking the consistency and universality of the gravitational suppression (GraS) hypothesis, a phenomenological model for a new interaction between dark matter and baryons. Motivated by the puzzle of the core versus cusp distribution of dark matter in the center of halos, this hypothesis claims to reconcile the predictions from N-body \Lambda cold dark matter simulations with kinematic observations. The GraS model improves the kinematic fitting residuals, but the mass parameters are unphysical and put the theory in difficulty.Comment: 4 pages, 3 figures, 1 tabl

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"

Evidence for a Massive Dark Object in NGC 4350

In this work we build a detailed dynamic model for a S0 galaxy possibly hosting a central massive dark object (MDO). We show that the photometric profiles and the kinematics along the major and minor axes, including the h3 and h4 profiles, imply the presence of a central MDO of mass M = 1.5 - 9.7 10^8 solar masses, i.e. 0.3-2.8% of the mass derived for the stellar spheroidal component. Models without MDO are unable to reproduce the kinematic properties of the inner stars and of the rapidly rotating nuclear gas. The stellar population comprise of an exponential disc (27% of the light) and a diffuse spheroidal component (73% of the light) that cannot be represented by a simple de Vaucouleurs profile at any radius. The M/L ratios we found for the stellar components (respectively 3.3 and 6.6) are typical of those of disc and elliptical galaxies.Comment: 9 pages, 4 encapsulated postscript figures. Requires mn.sty, psfig.sty. Accepted for publication in MNRA

The Disk Mass of Spiral Galaxies

We derive the disk masses of 18 spiral galaxies of different luminosity and Hubble Type, both by mass modelling their rotation curves and by fitting their SED with spectro-photometric models. The good agreement of the estimates obtained from these two different methods allows us to quantify the reliability of their performance and to derive very accurate stellar mass-to-light ratio vs color (and stellar mass) relationships.Comment: 5 pages, 4 Figures accepted to M