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Galactic winds and outflows are an ubiquitous phenomenon in galaxies with active star formation and/or active nuclei. They constitute the main mechanism for redistributing dust and metals on large scales and are therefore a key ingredient to understand the life cycle of galaxies. Among galaxies, ULIRGs are of particular interest in this context, as they host intense starbursts and are likely to be the dominant star formers at z > 1. These objects have been shown to host important winds, but it is not yet known what is the frequency of galactic winds and their properties in galaxies with lower star formation rates (SFR). We are studying galactic winds in a sample of 21 galaxies with different SFRs (including ULIRGs) from observations with the INTEGRAL fiber spectrograph on the 4.2m WHT. In order to be able to address the complex multi–phase nature of the wind phenomenon, we have used the Na I D doublet absorption lines to trace cold gas, and a few emission lines (Hα, [N ii] and [S ii]) to trace the warmer ionized gas of the wind. The distribution and kinematics of both components in these objects is then analysed. Preliminary results show strong spatial correlation between regions with high non–circular velocities, areas with high star formation activity and regions with two different components in the emission lines. This set of data will help us to characterise the distribution and kinematics of the winds and their relation with the host galaxy type.
We present the surface brightness profile fitting of a sample of double nucleus disk galaxies, minor merger candidates. We have decomposed these systems into two compact nuclear components and one or two extended galaxy disk components and estimated the luminosity of the primary and secondary nucleus and of the host galaxy and the separation between the two nuclei. Based on the ratio of nuclear luminosities we find that most of the sources qualify as major mergers despite their initial classification as minor merging systems. This is supported by the finding that 65% of the host galaxies are fitted only by one galaxy disk and that the luminosity of both the primary and the secondary nucleus decreases with decreasing nuclear separation, as expected from simulations of disk galaxy mergers. All these results indicate that these sources are most plausibly in the post-merger state of a major merger event. We also identify 19 candidates to binary active nucleus with nuclear separation ≤1 kpc.
Simple gravitational lens models usually suffice to reproduce the positions of lensed quasar images, but they have problems to reproduce their optical flux ratios. The so-called flux ratio anomalies are thought to be produced by small-scale structure in the lens galaxies (microlensing).
An invariant classification scheme of algebraically
general rotating dust with a purely electric Weyl tensor is
presented. It turns out that the vorticity vector of the dust
congruence is necessarily parallel to a Weyl principal vector, which
is moreover geodesic. An explicit metric expression can be obtained
for the subclass of expanding models with one functionally
independent zero-order Riemann invariant. The basic equations for
the general case, where there are two such invariants, are given
within a weighted 1+1+2 tetrad formalism.
We provide a covariant derivation of plasma physics coupled to gravitation by utilizing the 3+1 formulation of general relativity, including a discussion of the Lorentz force law. We then reduce the system to the spherically symmetric case and show that all regions of the spacetime can be represented in a single coordinate system, thus revoking the need for junction conditions. We further show that the region exterior to the collapsing region is naturally described by the charged Vaidya spacetime in non-null coordinates.
We show that the metric f(R) theory of gravitation proposed by
Sobouti (2007) predicts the existence of gravitational waves travelling
at the speed of light in vacuum. In fact, this is prooved in general
terms for all metric theories of gravity which can be expressed as powers
of Ricci's scalar R. We also show that an extra additional lensing
as compared to that predicted by standard general relativity is produced
in that theory.
The ESA astrometric mission Gaia (launch in late 2011) will be able to put
to test General Relativity (GR) also thanks to a differential experiment,
GAREX, implemented in the form of repeated Eddington-like measurement,
aiming at measuring, for the first time, the quadrupole light bending due to
an oblate planet.
Applications of Discrete Differential Forms in numerical GR are
described. The motivation to use this finite element method is
its manifest coordinate independence. It is discussed how numerical
schemes based on this method were developed and results of
simulations for spherically symmetric vacuum space-times are presented.
I summarize some of the observational phenomenology in compact X-ray
sources (neutron stars, stellar-mass black holes and super-massive
black holes) where X-ray observations reveal strong gravity in
action. Although there is no attempt to claim that these
observations constitute or might lead in the future to real tests of
General Relativity, they allow us to witness a variety of its
effects in the strong field limit.
We find that deviation from the virial equilibrium of the Abell Cluster A586 yields evidence of the interaction between dark matter and dark energy. We argue that this interaction
might imply a violation of the Equivalence Principle. These evidences are found in the context of two different models of dark energy-dark matter interaction.
f(R) gravity is attracting a lot of interest as alternative
candidates to explain the observed cosmic acceleration and the
missing matter in large scale structures. Very likely, what we
call “Dark Matter” and “Dark Energy” are nothing else but signals
of the breakdown of General Relativity at large scales. Besides,
Solar System experiments do not exclude, a priori, the possibility
that such theories could give small observable effects also at
these scales. We review some results giving the basic ingredients
of such an approach.
We present two results for bounding marginally
outer trapped surfaces (MOTSs) in Killing initial data satisfying the null
energy condition and containing an untrapped barrier.
The first one applies to the stationary case and
states that no bounding MOTS
lying in the
exterior region where the stationary Killing vector is causal and
penetrating into the timelike region can exist.
The second result applies to the static case
and shows that no bounding MOTS can
penetrate into the exterior region where
the static Killing vector is timelike.
These results extend an interesting theorem by P. Miao (Miao 2005).
Nowadays, Gravitational lensing is a fundamental tool to study the light propagation in the universe and the evolution of structures. Here, diferent forms of the Santos & Lima smoothness parameter as a funtion of cosmological redshift are used in order to describe various scenarios of evolution of structure. Its effects on the strong gravitational lensing SGL by galaxy cluster dark halos are analized in LCDM, EdS and OCDM cosmologies. The dark matter halos modeled by Navarro-Frenk-White singular profile and the Preses-Schechter approximation is assumed to describe its distribution. We found that SGL probability by galaxy clusters becomes to be sensible to the evolution of structures scenario considered for sources farther than z ≈ 2 and it strongly depends on the cosmology and the smoothness parameter actual value.
In this contribution we summarize some of our recent results about
the matching of collapsing inhomogeneous dust-filled spacetimes to
vacuum static exteriors with a negative cosmological constant in
planar or hyperbolic symmetry. This models gravitational collapse to
toroidal or higher genus asymptotically AdS black holes.
Although the Lanczos potential (a (2,1) form, Labc) for the
Weyl tensor does not exist in dimensions greater than four, a new
potential (a (2,3) form, Pabcde, which coincides with the
double dual of Labc in four dimensions) has recently been
shown to exist in all dimensions n ≥ 4.
In this talk we investigate the question of gauge and
discuss the structure of the new potential's wave equation which
is obtained from the Bianchi identities; identifying the gauge supplies us with a new direct proof of the existence of Pabcde via the Cauchy-Kowaleski theorem, as well as the foundation for more general investigations of the first order symmetric hyperbolic structure.
We report about our first tests and results in simulating the last phase of the coalescence and
the merger of binary relativistic stars. The simulations were performed using our code Whisky and mesh refinement through the Carpet driver.
The Hessian of the entropy function can be thought of as a metric
tensor on state space. In the context of thermodynamical
fluctuation theory Ruppeiner has argued that the Riemannian geometry
of this metric gives insight into the underlying statistical
mechanical system; the claim is supported by numerous examples. We
study these geometries for some families of black holes and find that
the Ruppeiner geometry is flat for Reissner–Nordström black holes
in any dimension, while curvature singularities occur for the Kerr
black holes. Kerr black holes have instead flat Weinhold curvature.
Global hyperbolicity is a classical and well-known concept, which
lies in the core of General Relativity. Here we discuss briefly
five approaches to this concept. They yield different definitions
which become natural in diverse contexts: the initial value
problem, singularity theorems, existence of maximizing causal
geodesics, possibility to split globally the spacetime, causal
boundaries. The neat formulation and definitive equivalence
between these definitions have been completed only recently. A
very brief summary is presented.