434 research outputs found
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 .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 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
Galactic Potentials
The information contained in galactic rotation curves is examined under a
minimal set of assumptions. If emission occurs from stable circular geodesic
orbits of a static spherically symmetric field, with information propagated to
us along null geodesics, observed rotation curves determine galactic potentials
without specific reference to any metric theory of gravity. Given the
potential, the gravitational mass can be obtained by way of an anisotropy
function of this field. The gravitational mass and anisotropy function can be
solved for simultaneously in a Newtonian limit without specifying any specific
source. This procedure, based on a minimal set of assumptions, puts very strong
constraints on any model of the "dark matter".Comment: A somewhat longer form of the final version to appear in Physical
Review Letters.Clarification and further reference
The Universal Rotation Curve of Spiral Galaxies. II The Dark Matter Distribution out to the Virial Radius
In the current LambdaCDM cosmological scenario, N-body simulations provide us
with a Universal mass profile, and consequently a Universal equilibrium
circular velocity of the virialized objects, as galaxies. In this paper we
obtain, by combining kinematical data of their inner regions with global
observational properties, the Universal Rotation Curve (URC) of disk galaxies
and the corresponding mass distribution out to their virial radius. This curve
extends the results of Paper I, concerning the inner luminous regions of Sb-Im
spirals, out to the edge of the galaxy halos.Comment: In press on MNRAS. 10 pages, 8 figures. The Mathematica code for the
figures is available at: http://www.novicosmo.org/salucci.asp Corrected typo
Dark Matter Scaling Relations
We establish the presence of a dark matter core radius, for the first time in
a very large number of spiral galaxies of all luminosities. Contrary to common
opinion we find that the sizes of these cores and the " DM core problem" are
bigger for more massive spirals. As a result the Burkert profile provides an
excellent mass model for dark halos around disk galaxies. Moreover, we find
that the spiral dark matter core densities and core radii
lie in the same scaling relation of dwarf galaxies with core radii upto ten times more
smaller.Comment: 4 pages, 4 figures, Accepted for Publication in Apj Let
The radial Tully-Fisher relation for spiral galaxies - I
We find a new Tully-Fisher-like relation for spiral galaxies holding at different galactocentric radii. This radial Tully-Fisher relation allows us to investigate the distribution of matter in the optical regions of spiral galaxies. This relation, applied to three different samples of rotation curves of spiral galaxies, directly proves that: (i) the rotation velocity of spirals is a good measure of their gravitational potential and both the rotation curve's amplitudes and profiles are well predicted by galaxy luminosity, (ii) the existence of a dark component, less concentrated than the luminous one, and (iii) a scaling law, according to which, inside the disc optical size: M-dark/M-lum = 0.5(L-B/10(11) L-B circle dot)(-0.7)
Galactic rotation curves in modified gravity with non-minimal coupling between matter and geometry
We investigate the possibility that the behavior of the rotational velocities
of test particles gravitating around galaxies can be explained in the framework
of modified gravity models with non-minimal matter-geometry coupling.
Generally, the dynamics of test particles around galaxies, as well as the
corresponding mass deficit, is explained by postulating the existence of dark
matter. The extra-terms in the gravitational field equations with
geometry-matter coupling modify the equations of motion of test particles, and
induce a supplementary gravitational interaction. Starting from the variational
principle describing the particle motion in the presence of the non-minimal
coupling, the expression of the tangential velocity of a test particle, moving
in the vacuum on a stable circular orbit in a spherically symmetric geometry,
is derived. The tangential velocity depends on the metric tensor components, as
well as of the coupling function between matter and geometry. The Doppler
velocity shifts are also obtained in terms of the coupling function. If the
tangential velocity profile is known, the coupling term between matter and
geometry can be obtained explicitly in an analytical form. The functional form
of this function is obtained in two cases, for a constant tangential velocity,
and for an empirical velocity profile obtained from astronomical observations,
respectively. Therefore, these results open the possibility of directly testing
the modified gravity models with non-minimal coupling between matter and
geometry by using direct astronomical and astrophysical observations at the
galactic or extra-galactic scale.Comment: 8 pages, accepted for publication in PR
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