1,901 research outputs found
Dark Matter Halos: The Dynamical Basis of Effective Empirical Models
We investigate the dynamical basis of the classic empirical models
(specifically, Sersic-Einasto and generalized NFW) that are widely used to
describe the distributions of collisionless matter in galaxies. We submit that
such a basis is provided by our \alpha-profiles, shown to constitute solutions
of the Jeans dynamical equilibrium with physical boundary conditions. We show
how to set the parameters of the empirical in terms of the dynamical models; we
find the empirical models, and specifically Sersic-Einasto, to constitute a
simple and close approximation to the dynamical models. Finally, we discuss how
these provide an useful baseline for assessing the impact of the small-scale
dynamics that may modulate the density slope in the central galaxy regions.Comment: 11 pages, 2 figures, Accepted by Advances in Astronom
The Intracluster Plasma: a Universal Pressure Profile?
The pressure profiles of the Intracluster Plasma in galaxy clusters show a
wide variance when observed in X rays at low redshifts z<0.2. We find the
profiles to follow two main patterns, featuring either a steep or a shallow
shape throughout both core and outskirts. We trace these shapes back to a
physical dichotomy of clusters into two classes, marked by either low entropy
(LE) or high entropy (HE) throughout. From X-ray observations and
Sunyaev-Zel'dovich stacked data at higher 0.2<z<0.4, we elicit evidence of an
increasing abundance of HEs relative to LEs. We propose this to constitute a
systematic trend toward high z; specifically, we predict the pressure profiles
to converge into a truly universal HE-like template for z>0.5. We submit our
physical templates and converging trend for further observational tests, in
view of the current and upcoming measurements of individual, stacked, and
integrated Sunyaev-Zel'dovich signals.Comment: 5 pages, 2 figures. Typos-corrected. Accepted by ApJ
Probing the Astrophysics of Cluster Outskirts
In galaxy clusters the entropy distribution of the IntraCluster Plasma
modulates the latter's equilibrium within the Dark Matter gravitational wells,
as rendered by our Supermodel. We argue the entropy production at the boundary
shocks to be reduced or terminated as the accretion rates of DM and
intergalactic gas peter out; this behavior is enforced by the slowdown in the
outskirt development at late times, when the Dark Energy dominates the
cosmology while the outer wings of the initial perturbation drive the growth.
In such conditions, we predict the ICP temperature profiles to steepen into the
cluster outskirts. The detailed expectations from our simple formalism agree
with the X-ray data concerning five clusters whose temperature profiles have
been recently measured out to the virial radius. We predict steep temperature
declines to prevail in clusters at low redshift, tempered only by rich environs
including adjacent filamentary structures.Comment: 4 pages, 3 figures, uses aa.cls. Typos corrected. Accepted by A&A
Two phase galaxy formation: The Evolutionary Properties of Galaxies
We use our model for the formation and evolution of galaxies within a
two-phase galaxy formation scenario, showing that the high-redshift domain
typically supports the growth of spheroidal systems, whereas at low redshifts
the predominant baryonic growth mechanism is quiescent and may therefore
support the growth of a disc structure. Under this framework we investigate the
evolving galaxy population by comparing key observations at both low and
high-redshifts, finding generally good agreement. By analysing the evolutionary
properties of this model, we are able to recreate several features of the
evolving galaxy population with redshift, naturally reproducing number counts
of massive star-forming galaxies at high redshifts, along with the galaxy
scaling relations, star formation rate density and evolution of the stellar
mass function. Building upon these encouraging agreements, we make model
predictions that can be tested by future observations. In particular, we
present the expected evolution to z=2 of the super-massive black hole mass
function, and we show that the gas fraction in galaxies should decrease with
increasing redshift in a mass, with more and more evolution going to higher and
higher masses. Also, the characteristic transition mass from disc to bulge
dominated system should decrease with increasing redshift.Comment: 15 pages, 11 figures. Version polished for publication in MNRA
Intracluster Entropy from Joint X-ray and Sunyaev-Zel'dovich Observations
The temperature and density of the hot diffuse medium pervading galaxy groups and clusters combine into one significant quantity, the entropy. Here we express the entropy levels and profiles in model-independent forms by joining two observables, the X-ray luminosity and the change in the CMB intensity due to the Sunyaev-Zel'dovich (SZ) effect. Thus we present both global scaling relations for the entropy levels from clusters and groups, and a simple expression yielding the entropy profiles in individual clusters from resolved X-ray surface brightness and SZ spatial distributions. We propose that our approach provides two useful tools for comparing large data samples with models, in order to probe the processes that govern the thermal state of the hot intracluster medium. The feasibility of using such a diagnostic for the entropy is quantitatively assessed, based on current X-ray and upcoming SZ measurements
Europe: from National-State Borders to Cultural and Religious Identitaries Borders
Contemporary Europe is not anymore characterized by traditional National-State borders, but rather by new borders within National-State borders. These new borders arise by cultural, ethnic and religious identity claimed by national and non-national citizens who live in the same public space. Therefore, these new borders are not territorial borders, such as those, which divide a state from another, but rather identitaries borders. The fact that even territorial borders are nowadays less strong is a problem for law. Indeed, law needs a territory, which is a space with borders where the rules of a legal system are in force. The aim of this paper will be to focus on how the law manages the phenomenon of strengthening of the identirary borders in order to understand what are the solutions that states give to identity making claims
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
Self-Similar Dynamical Relaxation of Dark Matter Halos in an Expanding Universe
We investigate the structure of cold dark matter halos using advanced models
of spherical collapse and accretion in an expanding Universe. These base on
solving time-dependent equations for the moments of the phase-space
distribution function in the fluid approximation; our approach includes
non-radial random motions, and most importantly, an advanced treatment of both
dynamical relaxation effects that takes place in the infalling matter:
phase-mixing associated to shell crossing, and collective collisions related to
physical clumpiness. We find self-similar solutions for the
spherically-averaged profiles of mass density rho(r), pseudo phase-space
density Q(r) and anisotropy parameter beta(r). These profiles agree with the
outcomes of state-of-the-art N-body simulations in the radial range currently
probed by the latter; at smaller radii, we provide specific predictions. In the
perspective provided by our self-similar solutions we link the halo structure
to its two-stage growth history, and propose the following picture. During the
early fast collapse of the inner region dominated by a few merging clumps,
efficient dynamical relaxation plays a key role in producing a closely
universal mass density and pseudo phase-space density profiles; in particular,
these are found to depend only weakly on the detailed shape of the initial
perturbation and the related collapse times. The subsequent inside-out growth
of the outer regions feeds on the slow accretion of many small clumps and
diffuse matter; thus the outskirts are only mildly affected by dynamical
relaxation but are more sensitive to asymmetries and cosmological variance.Comment: 31 pages, 16 figures. Typos corrected. Accepted by Ap
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