9,570 research outputs found
Two-dimensional kinematics of SLACS lenses: III. Mass structure and dynamics of early-type lens galaxies beyond z ~ 0.1
We combine in a self-consistent way the constraints from both gravitational
lensing and stellar kinematics to perform a detailed investigation of the
internal mass distribution, amount of dark matter, and dynamical structure of
the 16 early-type lens galaxies from the SLACS Survey, at z = 0.08 - 0.33, for
which both HST/ACS and NICMOS high-resolution imaging and VLT VIMOS IFU
spectroscopy are available. Based on this data set, we analyze the inner
regions of the galaxies, i.e. typically within one (3D) effective radius r_e,
under the assumption of axial symmetry and by constructing dynamical models
supported by two-integral stellar DFs. For all systems, the total mass density
distribution is found to be well approximated by a simple power-law: this
profile is on average slightly super-isothermal, with a logarithmic slope
= 2.074^{+0.043}_{-0.041} (68% CL) and an intrinsic scatter
0.144^{+0.055}_{-0.014}, and is fairly round, with an average axial ratio =
0.77+/-0.04. The lower limit for the dark matter fraction (fDM) inside r_e
ranges, in individual systems, from nearly zero to almost a half, with a median
value of 12%. By including stellar masses derived from SPS models with a
Salpeter IMF, we obtain an average fDM = 31%. The fDM rises to 61% if, instead,
a Chabrier IMF is assumed. For both IMFs, the dark matter fraction increases
with the total mass of the galaxy (3-sigma correlation). Based on the intrinsic
angular momentum parameter calculated from our models, we find that the
galaxies can be divided into two dynamically distinct groups, which are shown
to correspond to the usual classes of the slow and fast rotators. Overall, the
SLACS systems are structurally and dynamically very similar to their nearby
counterparts, indicating that the inner regions of early-type galaxies have
undergone little, if any, evolution since redshift z ~ 0.35. (Abridged)Comment: 27 pages, 34 figures. MNRAS, in pres
The forward kinematics of doubly-planar Gough-Stewart platforms and the position analysis of strips of tetrahedra
The final publication is available at link.springer.comA strip of tetrahedra is a tetrahedron-tetrahedron truss where any tetrahedron has two neighbors except those in the extremes which have only one. The problem of finding all the possible lengths for an edge in the strip compatible with a given distance imposed between the strip end-points has been revealed of relevance due to the large number of possible applications. In this paper, this is applied to solve the forward kinematics of 6-6 Gough-Stewart platforms with planar base and moving platform, a problem which is known to have up to 40 solutions (20 if we do not consider mirror configurations with respect to the base as different solutions).Peer ReviewedPostprint (author's final draft
The evolution of galaxy groups and of galaxies therein
Properties of groups of galaxies depend sensitively on the algorithm for
group selection, and even the most recent catalogs of groups built from
redshift-space selection should suffer from projections and infalling galaxies.
The cosmo-dynamical evolution of groups from initial Hubble expansion to
collapse and virialization leads to a fundamental track (FT) in
virial-theorem-M/L vs crossing time. The increased rates of mergers, both
direct and after dynamical friction, in groups relative to clusters, explain
the higher fraction of elliptical galaxies at given local number density in
X-ray selected groups, relative to clusters, even when the hierarchical
evolution of groups is considered. Galaxies falling into groups and clusters
should later travel outwards to typically 2 virial radii, which is somewhat
less than the outermost radius where observed galaxy star formation
efficiencies are enhanced relative to field galaxies of same morphological
type. An ongoing analysis of the internal kinematics of X-ray selected groups
suggests that the radial profiles of line of sight velocity dispersion are
consistent with isotropic NFW distributions for the total mass density, with
higher (lower) concentrations than LambdaCDM predictions in groups of high
(low) mass. The critical mass, at M200 ~ 10^13 M_sun is consistent with
possible breaks in the X-ray luminosity-temperature and Fundamental Plane
relations. The internal kinematics of groups indicate that the M-T relation of
groups should agree with that extrapolated from clusters with no break at the
group scale. The analyses of observed velocity dispersion profiles and of the
FT both suggest that low velocity dispersion groups (compact and loose, X-ray
emitting or undetected) are quite contaminated by chance projections.Comment: Invited review, ESO workshop "Groups of Galaxies in the Nearby
Universe", held in Santiago, Chile, 5-9 December 2005, ed. I. Saviane, V.
Ivanov & J. Borissova, 16 page
Theoretical Models of the Galactic Bulge
Near infrared images from the COBE satellite presented the first clear
evidence that our Milky Way galaxy contains a boxy shaped bulge. Recent years
have witnessed a gradual paradigm shift in the formation and evolution of the
Galactic bulge. Bulges were commonly believed to form in the dynamical violence
of galaxy mergers. However, it has become increasingly clear that the main body
of the Milky Way bulge is not a classical bulge made by previous major mergers,
instead it appears to be a bar seen somewhat end-on. The Milky Way bar can form
naturally from a precursor disk and thicken vertically by the internal
firehose/buckling instability, giving rise to the boxy appearance. This picture
is supported by many lines of evidence, including the asymmetric parallelogram
shape, the strong cylindrical rotation (i.e., nearly constant rotation
regardless of the height above the disk plane), the existence of an intriguing
X-shaped structure in the bulge, and perhaps the metallicity gradients. We
review the major theoretical models and techniques to understand the Milky Way
bulge. Despite the progresses in recent theoretical attempts, a complete bulge
formation model that explains the full kinematics and metallicity distribution
is still not fully understood. Upcoming large surveys are expected to shed new
light on the formation history of the Galactic bulge.Comment: Invited review to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing, 2015, in press. 27 pages, 7
figure
Pure Gravities via Color-Kinematics Duality for Fundamental Matter
We give a prescription for the computation of loop-level scattering
amplitudes in pure Einstein gravity, and four-dimensional pure supergravities,
using the color-kinematics duality. Amplitudes are constructed using double
copies of pure (super-)Yang-Mills parts and additional contributions from
double copies of fundamental matter, which are treated as ghosts. The
opposite-statistics states cancel the unwanted dilaton and axion in the bosonic
theory, as well as the extra matter supermultiplets in supergravities. As a
spinoff, we obtain a prescription for obtaining amplitudes in supergravities
with arbitrary non-self-interacting matter. As a prerequisite, we extend the
color-kinematics duality from the adjoint to the fundamental representation of
the gauge group. We explain the numerator relations that the fundamental
kinematic Lie algebra should satisfy. We give nontrivial evidence supporting
our construction using explicit tree and loop amplitudes, as well as more
general arguments.Comment: 48 pages + refs, 15 figures, 3 tables; v2 minor corrections, journal
versio
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