1,045 research outputs found
Homeoidally striated density profiles: sequences of virial equilibrium configurations with constant anisotropy parameters
The formulation of the tensor virial equations is generalized to unrelaxed
configurations, where virial equilibrium does not coincide with dynamical (or
hydrostatic) equilibrium. Further investigation is devoted to special classes
of homeoidally striated ellipsoids, defined as homeoidally striated, Jacobi
ellipsoids. In particular, virial equilibrium configurations with constant
anisotropy parameters are studied with more detail, including both flattened
and elongated, triaxial configurations, and the determination of the related
bifurcation points. The explicit expression of different rotation parameters is
also determined. An application is made to dark matter haloes hosting giant,
galaxies, with regard to assigned initial and final configuration, following
and generalizing to many respects a procedure conceived by Thuan & Gott (1975).
The dependence of the limiting axis ratios, below which no configuration is
allowed for the sequence under consideration, on the change in mass, total
energy, and angular momentum, during the evolution, is illustrated in some
representative situations. The dependence of axis ratios and rotation
parameters on an additional parameter, related to the initial conditions of the
density perturbation, is analysed in connection with a few special cases.
Within the range of Peebles (1969) rotation parameter, inferred from
high-resolution numerical simulations, the shape of dark matter haloes is
mainly decided by the amount of anisotropy in residual velocity distribution.
On the other hand, the contribution of rotation has only a minor effect on the
meridional plane, and no effect on the equatorial plane, as bifurcation points
occur for larger values of Peebles (1969) rotation parameter. To this respect,
dark matter haloes are found to resemble giant elliptical galaxies.Comment: 43 pages, 8 figures, 6 tables; a reduced version has been accepted
for publication on A
R fluids
A theory of collisionless fluids is developed in a unified picture, where
nonrotating figures with anisotropic random velocity component distributions
and rotating figures with isotropic random velocity component distributions,
make adjoints configurations to the same system. R fluids are defined and mean
and rms angular velocities and mean and rms tangential velocity components are
expressed, by weighting on the moment of inertia and the mass, respectively.
The definition of figure rotation is extended to R fluids. The generalized
tensor virial equations are formulated for R fluids and further attention is
devoted to axisymmetric configurations where, for selected coordinate axes, a
variation in figure rotation has to be counterbalanced by a variation in
anisotropy excess and vice versa. A microscopical analysis of systematic and
random motions is performed under a few general hypotheses, by reversing the
sign of tangential or axial velocity components of an assigned fraction of
particles, leaving the distribution function and other parameters unchanged
(Meza 2002). The application of the reversion process to tangential velocity
components, implies the conversion of random motion rotation kinetic energy
into systematic motion rotation kinetic energy. The application of the
reversion process to axial velocity components, implies the conversion of
random motion translation kinetic energy into systematic motion translation
kinetic energy, and the loss related to a change of reference frame is
expressed in terms of systematic (imaginary) motion rotation kinetic energy. A
procedure is sketched for deriving the spin parameter distribution (including
imaginary rotation) from a sample of observed or simulated large-scale
collisionless fluids i.e. galaxies and galaxy clusters.Comment: 29 pages, 2 figure
Virialization of matter overdensities within dark energy subsystems: special cases
The virialization of matter overdensities within dark energy subsystems is
considered under the restrictive assumptions (i) spherical-symmetric density
profiles, (ii) time-independent quintessence equation of state parameter, w,
and (iii) nothing but gravitational interaction between dark energy scalar
field and matter. In addition, the quintessence subsystem is conceived as made
of ``particles'' whose mutual interaction has intensity equal to G(1+3w) and
scales as the inverse square of their distance. Then the virial theorem is
formulated for subsystems. In the special case of fully clustered quintessence,
energy conservation is assumed with regard to either the whole system (global
energy conservation), or to the matter subsystem within the tidal potential
induced by the quintessence subsystem (partial energy conservation). Further
investigation is devoted to a few special values, w=-1/3, -1/2, -2/3, -1. The
special case of fully clustered (i.e. collapsing together with the matter)
quintessence is studied in detail. The general case of partially clustered
quintessence is considered in terms of a degree of quintessence de-clustering,
\zeta, ranging from fully clustered (\zeta=0) to completely de-clustered
(\zeta=1) quintessence, respectively. The special case of unclustered (i.e.
remaining homogeneous) quintessence is also discussed. The trend exhibited by
the fractional (virialization to turnaround) radius, \eta, as a function of
other parameters, is found to be different from its counterparts reported in
earlier attempts. The reasons of the above mentioned discrepancy are discussed.Comment: 44 pages, 8 figure
Clausius' Virial vs. Total Potential Energy in the dynamics of a two-component system
In a gravitational virialized bound system built up of two components, one of
which is embedded in the other, the Clausius' virial energy of one subcomponent
is not, in general, equal to its total potential energy, as occurs in a single
system without external forces. This is the main reason for the presence, in
the case of two non-coinciding concentric spheroidal subsystems, of a minimum
(in absolute value) in the Clausius' virial of the inner component B, when it
assumes a special configuration characterized by a value of its semi-major axis
we have named "tidal radius". The physical meaning, connected with its
appearance, is to introduce a scale length on the gravity field of the inner
subsystem, which is induced from the outer one. Its relevance in the galaxy
dynamics has been stressed by demonstrating that some of the main features of
the Fundamental Plane may follow as consequence of its existence. More physical
insight into the dynamics of a two component system may be got by looking at
the location of this scale length inside the plots of the potential energies of
each subsystem and of the whole system and by also taking into account the
trend of the anti-symmetric residual-energy, that is the difference between the
tidal and the interaction-energy of each component. Some thermodynamical
arguments related to the inner component are also added to prove as special is
the "tidal radius configuration". Moreover the role of the divergency at the
center of the two subsystems in obtaining this scale length is considered. For
the sake of simplicity the analysis has been performed in the case of a frozen
external component even if this constraint does not appear to be too relevant
in order to preserve the main results.Comment: New Astronomy, accepte
Simple MCBR models of chemical evolution: an application to the thin and the thick disk
Simple MCBR models of chemical evolution are extended to the limit of
dominant gas inflow or outflow with respect to gas locked up into long-lived
stars and remnants. For an assigned empirical differential oxygen abundance
distribution, which can be linearly fitted, a family of theoretical curves is
built up with assigned prescriptions. For curves with increasing cut parameter,
the gas mass fraction locked up into long-lived stars and remnants is found to
attain a maximum and then decrease towards zero as the flow tends to infinity,
while the remaining parameters show a monotonic trend. The theoretical integral
oxygen abundance distribution is also expressed. An application is performed to
the empirical distribution deduced from two different samples of disk stars,
for both the thin and the thick disk. The constraints on formation and
evolution are discussed in the light of the model. The evolution is tentatively
subdivided into four stages, A, F, C, E. The empirical distribution related to
any stage is fitted by all curves for a wide range of the cut parameter. The F
stage may safely be described by a steady inflow regime, implying a flat
theoretical distribution, in agreement with the results of hydrodynamical
simulations. Finally, (1) the change of fractional mass due to the extension of
the linear fit to the empirical distribution, towards both the (undetected)
low-metallicity and high-metallicity tail, is evaluated and (2) the idea of a
thick disk-thin disk collapse is discussed, in the light of the model.Comment: 31 pages, 9 tables and 4 figures; accepted for publication on Serbian
Astronomical Journa
O and Fe abundance correlations and distributions inferred for the thick and thin disk
A linear [Fe/H]-[O/H] relation is found for different stellar populations in
the Galaxy (halo, thick disk, thin disk) from a data sample obtained in a
recent investigation (Ram{\'\i}rez et al. 2013). These correlations support
previous results inferred from poorer samples: stars display a "main sequence"
expressed as [Fe/H] = [O/H where a unit slope, ,
implies a constant [O/Fe] abundance ratio. Oxygen and iron empirical abundance
distributions are then determined for different subsamples, which are well
explained by the theoretical predictions of multistage closed-(box+reservoir)
(MCBR) chemical evolution models by taking into account the found correlations.
The interpretation of these distributions in the framework of MCBR models gives
us clues about inflow/outflow rates in these different Galactic regions and
their corresponding evolution. Outflow rate for the thick and the thin disks
are lower than the halo outflow rate. Moreover if the thin disk built up from
the thick disk, both systems result of comparable masses. Besides that, the
iron-to-oxygen yield ratio and the primary to not primary contribution ratio
for the iron production are obtained from the data, resulting consistent with
SNII progenitor nucleosynthesis and with the iron production from SNIa
supernova events.Comment: 44 pages, 12 tables and 8 figures. A reduced version of the current
paper has been accepted for publication on SA
An application of the tensor virial theorem to hole + vortex + bulge systems
The tensor virial theorem for subsystems is formulated for three-component
systems and further effort is devoted to a special case where the inner
subsystems and the central region of the outer one are homogeneous, the last
surrounded by an isothermal homeoid. The virial equations are explicitly
written under additional restrictions. An application is made to hole + vortex
+ bulge systems, in the limit of flattened inner subsystems. Using the
Faber-Jackson relation, the standard - form is deduced
from qualitative considerations. The projected bulge velocity dispersion to
projected vortex velocity ratio, , as a function of the fractional
radius, y_{\rm BV}, and the fractional masses, , and ,
is plotted for several cases. It is shown that a fixed value of below
the maximum corresponds to two different configurations: a compact bulge on the
left and an extended bulge on the right. In addition, for fixed or
, and , more massive bulges are related to larger
and vice versa. The model is applied to NGC 4374 and NGC 4486, and the
bulge mass is inferred and compared with results from different methods. In
presence of a massive vortex , the hole mass has to be reduced
by a factor 2-3 with respect to the case of a massless vortex, to get the fit.Comment: 29 pages, 2 tables, and 5 figure
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