49 research outputs found
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
The mass distribution in Spirals
In the past years a wealth of observations has unraveled the structural
properties of the Dark and Luminous mass distribution in spirals. These have
pointed out to an intriguing scenario not easily explained by present theories
of galaxy formation. The investigation of individual and coadded objects has
shown that the spiral rotation curves follow, from their centers out to their
virial radii, a Universal profile (URC) that arises from the tuned combination
of a stellar disk and of a dark halo. The importance of the latter component
decreases with galaxy mass. Individual objects, on the other hand, have clearly
revealed that the dark halos encompassing the luminous discs have a constant
density core. This resulting observational scenario poses important challenges
to presently favored theoretical CDM Cosmology.Comment: Version matching the Proceedings of the CRAL-IPNL conference "Dark
Energy and Dark Matter", Lyon, 2008, references updated, an useful link
provide
DMAW 2010 LEGACY the Presentation Review: Dark Matter in Galaxies with its Explanatory Notes
The Seminar "Dark Matter in Galaxies" was delivered, within the Dark Matter
Awareness Week (1-8 December 2010) at 140 institutes in 46 countries and it was
followed by 4200 people. A documentation of this worldwide initiative is at
http://www.youtube.com/watch?v=AOBit8a-1Fw. A reference presentation, prepared
by a coordinated pool of leading scientists in the field, was available to
speakers. In response to feedbacks and suggestions, we upgraded it to a
"Presentation Review" of which we provide here the Explanatory Notes, the link
to the .pptx file, and some image of the slides. This Presentation Review is an
innovative scientific product to meet the request of information about the
phenomenology of the DM mystery at galactic scale. This Review concerns the
mass discrepancy phenomenon detected in galaxies, usually accounted by
postulating the presence of a non luminous non baryonic component. In the
theoretical framework of Newtonian Gravity we recall the properties of Dark
Matter halos as emerging from the state-of-the-art of numerical simulations
performed in the current scenario. Then, the simple but
much-telling phenomenology of the distribution of dark and luminous matter in
Spirals, Ellipticals, and dwarf Spheroidals is reported. We show that a
coherent observational framework emerges from reliable data of different large
samples of objects and it is obtained by different methods of investigation. We
then highlight the impressive evidence that the distribution of dark and
luminous matter are closely correlated and that have universal features. Hints
on the cosmological role of this phenomenological scenario are then given.
Finally, we discuss the constraints on the elusive nature of the dark particle
that the actual distribution of DM around galaxies pose on its direct and
indirect searches.Comment: 29 pages, 1 Figure, 1 List. The .pptx file of the Presentation can be
downloaded at http://www.sissa.it/ap/dmg/dmaw_presentation.htm
A constant dark matter halo surface density in galaxies
We confirm and extend the recent finding that the central surface density
r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core
radius and central density, is nearly constant and independent of galaxy
luminosity. Based on the co-added rotation curves of about 1000 spiral
galaxies, mass models of individual dwarf irregular and spiral galaxies of late
and early types with high-quality rotation curves and, galaxy-galaxy weak
lensing signals from a sample of spiral and elliptical galaxies, we find that
log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the
observed kinematics of Local Group dwarf spheroidal galaxies are consistent
with this value. Our results are obtained for galactic systems spanning over 14
magnitudes, belonging to different Hubble Types, and whose mass profiles have
been determined by several independent methods. In the same objects, the
approximate constancy of rho_0*r_0 is in sharp contrast to the systematical
variations, by several orders of magnitude, of galaxy properties, including
rho_0 and central stellar surface density.Comment: Accepted for publication in MNRAS. 9 pages, 4 figure
Analysis of Rotation Curves in the framework of R^n gravity
We present an analysis of a devised sample of Rotation Curves (RCs), aimed at
checking the consequences of a modified f(R) gravity on galactic scales.
Originally motivated by the the dark energy mystery, this theory may serve as a
possibility of explaining the observed non-Keplerian profiles of galactic RCs
in terms of a break-down of the Einstein General Relativity. We show that in
general the power-law f(R) version could fit well the observations with
reasonable values for the mass model parameters, encouraging further
investigation on R^n gravity from both observational and theoretical points of
view.Comment: Accepted for publication on Mon.Not.Roy.Astron.So
Galactic orbital motions in the Dark Matter, MOdified Newtonian Dynamics and MOdified Gravity scenarios
We simultaneously integrate in a numerical way the equations of motion of
both the Magellanic Clouds (MCs) in MOND, MOG and CDM for -1 <= t <= +1 Gyr to
see if, at least in principle, it is possible to discriminate between them
(Abridged version).Comment: LaTex2e, 11 pages, 2 tables, 8 figures. Issues concerning the masses
of MCs clarified. Integration time changed to -1 Gyr <= t <= +1 Gyr. To
appear in Monthly Notices of the Royal Astronomical Society (MNRAS
Dark energy and dust matter phases from an exact -cosmology model
We show that dust matter-dark energy combined phases can be achieved by the
exact solution derived from a power law cosmological model. This example
answers the query by which a dust-dominated decelerated phase, before
dark-energy accelerated phase, is needed in order to form large scale
structures.Comment: 6 pages, 5 figures. to appear in Phys. Lett.
Probing the dark matter issue in f(R)-gravity via gravitational lensing
For a general class of analytic f(R)-gravity theories, we discuss the weak
field limit in view of gravitational lensing. Though an additional Yukawa term
in the gravitational potential modifies dynamics with respect to the standard
Newtonian limit of General Relativity, the motion of massless particles results
unaffected thanks to suitable cancellations in the post-Newtonian limit. Thus,
all the lensing observables are equal to the ones known from General
Relativity. Since f(R)-gravity is claimed, among other things, to be a possible
solution to overcome for the need of dark matter in virialized systems, we
discuss the impact of our results on the dynamical and gravitational lensing
analyses. In this framework, dynamics could, in principle, be able to reproduce
the astrophysical observations without recurring to dark matter, but in the
case of gravitational lensing we find that dark matter is an unavoidable
ingredient. Another important implication is that gravitational lensing, in the
post-Newtonian limit, is not able to constrain these extended theories, since
their predictions do not differ from General Relativity.Comment: 7 pages, accepted for publication in EPJ
The dark matter density at the Sun's location
Aims: We derive the value of the dark matter density at the Sun's location (Ïâ) without fully modeling the mass distribution in the Galaxy. Methods: The proposed method relies on the local equation of centrifugal equilibrium and is independent of i) the shape of the dark matter density profile, ii) knowledge of the rotation curve from the galaxy center out to the virial radius, and iii) the uncertainties and the non-uniqueness of the bulge/disk/dark halo mass decomposition. Results: The result can be obtained in analytic form, and it explicitly includes the dependence on the relevant observational quantities and takes their uncertainties into account. By adopting the reference, state-of-the-art values for these, we find Ï â = 0.43(11)(10) GeV/cm3, where the quoted uncertainties are respectively due to the uncertainty in the slope of the circular-velocity at the Sun location and the ratio between this radius and the length scale of the stellar exponential thin disk. Conclusions: We obtained a reliable estimate of Ïâ, that, in addition has the merit of being ready to take any future change/improvement into account in the measures of the observational quantities it depends on