35 research outputs found
Gravity with extra dimensions and dark matter interpretation: Phenomenological example via Miyamoto-Nagai galaxy
A configuration whose density profile coincides with the Newtonian potential
for spiral galaxies is constructed from a 4D isotropic metric plus extra
dimensional components. A Miyamoto-Nagai ansatz is used to solve Einstein
equations. The stable rotation curves of such system are computed and, without
fitting techniques, we recover with accuracy the observational data for flat or
not asymptotically flat galaxy rotation curves. The density profiles are
reconstructed and compared to that obtained from the Newtonian potential.Comment: 10 pages, 10 figures, submitted to Brazilian Journal of Physic
Modified Newtonian Dynamics as an Alternative to Dark Matter
Modified Newtonian dynamics (MOND) is an empirically motivated modification
of Newtonian gravity or inertia suggested by Milgrom as an alternative to
cosmic dark matter. The basic idea is that at accelerations below a0 ~ 10^{-8}
cm/s^2 ~ cH0/6 the effective gravitational attraction approaches sqrt{gN*a0}
where gN is the usual Newtonian acceleration. This simple algorithm yields flat
rotation curves for spiral galaxies and a mass-rotation velocity relation of
the form M ~ V^4 that forms the basis for the observed luminosity-rotation
velocity relation-- the Tully-Fisher law. We review the phenomenological
success of MOND on scales ranging from dwarf spheroidal galaxies to
superclusters, and demonstrate that the evidence for dark matter can be equally
well interpreted as evidence for MOND. We discuss the possible physical basis
for an acceleration-based modification of Newtonian dynamics as well as the
extension of MOND to cosmology and structure formation.Comment: To be published in volume 40 of Annual Reviews of Astronomy &
Astrophysics. 36 pages plus 12 figures and 1 tabl
Rotation Curves of Spiral Galaxies
Rotation curves of spiral galaxies are the major tool for determining the
distribution of mass in spiral galaxies. They provide fundamental information
for understanding the dynamics, evolution and formation of spiral galaxies. We
describe various methods to derive rotation curves, and review the results
obtained. We discuss the basic characteristics of observed rotation curves in
relation to various galaxy properties, such as Hubble type, structure,
activity, and environment.Comment: 40 pages, 6 gif figures; Ann. Rev. Astron. Astrophys. Vol. 39, p.137,
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The first and second data releases of the Kilo-Degree Survey
Context. The Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will image 1500 square degrees in four filters (ugri), and together with its near-infrared counterpart VIKING will produce deep photometry in nine bands. Designed for weak lensing shape and photometric redshift measurements, its core science driver is mapping the large-scale matter distribution in the Universe back to a redshift of ~0.5. Secondary science cases include galaxy evolution, Milky Way structure, and the detection of high-redshift clusters and quasars.
Aims. KiDS is an ESO Public Survey and dedicated to serving the astronomical community with high-quality data products derived from the survey data. Public data releases, the first two of which are presented here, are crucial for enabling independent confirmation of the survey’s scientific value. The achieved data quality and initial scientific utilization are reviewed in order to validate the survey data.
Methods. A dedicated pipeline and data management system based on ASTRO-WISE, combined with newly developed masking and source classification tools, is used for the production of the data products described here. Science projects based on these data products and preliminary results are outlined.
Results. For 148 survey tiles (≈160 sq.deg.) stacked ugri images have been released, accompanied by weight maps, masks, source lists, and a multi-band source catalogue. Limiting magnitudes are typically 24.3, 25.1, 24.9, 23.8 (5σ in a 2′′ aperture) in ugri, respectively, and the typical r-band PSF size is less than 0.7′′. The photometry prior to global homogenization is stable at the ~2% (4%) level in gri (u) with some outliers due to non-photometric conditions, while the astrometry shows a typical 2D rms of 0.03′′. Early scientific results include the detection of nine high-z QSOs, fifteen candidate strong gravitational lenses, high-quality photometric redshifts and structural parameters for hundreds of thousands of galaxies
The Mass Distribution and Rotation Curve in the Galaxy
The mass distribution in the Galaxy is determined by dynamical and
photometric methods. Rotation curves are the major tool for determining the
dynamical mass distribution in the Milky Way and spiral galaxies. The
photometric (statistical) method utilizes luminosity profiles from optical and
infrared observations, and assumes empirical values of the mass-to-luminosity
(M/L) ratio to convert the luminosity to mass. In this chapter the dynamical
method is described in detail, and rotation curves and mass distribution in the
Milky Way and nearby spiral galaxies are presented. The dynamical method is
categorized into two methods: the decomposition method and direct method. The
former fits the rotation curve by calculated curve assuming several mass
components such as a bulge, disk and halo, and adjust the dynamical parameters
of each component. Explanations are given of the mass profiles as the de
Vaucouleurs law, exponential disk, and dark halo profiles inferred from
numerical simulations. Another method is the direct method, with which the mass
distribution can be directly calculated from the data of rotation velocities
without employing any mass models. Some results from both methods are
presented, and the Galactic structure is discussed in terms of the mass.
Rotation curves and mass distributions in external galaxies are also discussed,
and the fundamental mass structures are shown to be universal.Comment: 54 pages, 25 figures, in 'Planets, Stars and Stellar Systems',
Springer, Vol. 5, ed. G. Gilmore, Chap. 19. Note: Preprint with full figures
is available from http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2013psss
3.5 keV X-ray line signal from decay of right-handed neutrino due to transition magnetic moment
MODIFIED DYNAMICS (MOND) AS A DARK HALO
We propose a form for dark haloes that embodies the fundamental aspect of Milgrom's modified dynamics (MOND): the discrepancy between the visible mass and the Newtonian dynamical mass appears below a critical acceleration. This is a halo having a density distribution, at least to several tens of kpc, of the form Sigma(0)/r, where Sigma(0), is a constant of surface density which does not vary from galaxy to galaxy. To avoid rising rotation curves, such a density distribution must obviously steepen beyond some radius, and we have chosen the Hernquist model in which the density falls as 1/r(4) beyond a characteristic scale. We show that, assuming that the visible (baryonic) matter is some constant fraction of the dark matter, spiral galaxies with such haloes exhibit a Tully-Fisher law of the observed form. In a sample of 10 spiral galaxies with well-determined extended rotation curves this halo, combined with the observable matter, can successfully model the observed curves. Moreover, in the seven most luminous galaxies, the best-fitting models have about the same value of Sigma(0) and are effectively one-parameter fits as in MOND (mass-to-light of the visible disc). The one-parameter description, however, does break down for the three dwarf galaxies in the sample with the lowest internal accelerations