833 research outputs found
3D simulations of the early stages of AGN jets: geometry, thermodynamics and backflow
We investigate the interplay between jets from Active Galactic Nuclei (AGNs)
and the surrounding InterStellar Medium (ISM) through full 3D, high resolution,
Adaptive Mesh Refinement simulations performed with the FLASH code. We follow
the jet- ISM system for several Myr in its transition from an early, compact
source to an extended one including a large cocoon. During the jet evolution,
we identify three major evolutionary stages and we find that, contrary to the
prediction of popular theoretical models, none of the simulations shows a
self-similar behavior. We also follow the evolution of the energy budget, and
find that the fraction of input power deposited into the ISM (the AGN coupling
constant) is of order of a few percent during the first few Myr. This is in
broad agreement with galaxy formation models employing AGN feedback. However,
we find that in these early stages, this energy is deposited only in a small
fraction (< 1%) of the total ISM volume. Finally we demonstrate the relevance
of backflows arising within the extended cocoon generated by a relativistic AGN
jet within the ISM of its host galaxy, previously proposed as a mechanism for
self-regulating the gas accretion onto the central object. These backflows tend
later to be destabilized by the 3D dynamics, rather than by hydrodynamic
(Kelvin- Helmholtz) instabilities. Yet, in the first few hundred thousand
years, backflows may create a central accretion region of significant extent,
and convey there as much as a few millions of solar masses.Comment: Accepted in MNRAS - 16 pages, 12 figures - Multimedia available on
the author's webpage: http://www.mpia.de/~ciel
The influence of dynamical friction on the collapse of spherical density pertubation
We solve numerically the equations of motion for the collapse of a shell of baryonic matter falling into the central regions of a cluster of galaxies, taking into account of the presence of the substructure inducing dynamical friction. The evolution of the expansion parameter a(t) of the perturbation is calculated in spherical systems. The effect of dynamical friction is to reduce the binding radius and the total mass accreted by the central regions. Using a peak density profile given by Bardeen et al. (1986) we show how the binding radius of the perturbation is modified by dinamical friction. We show how dynamical friction modifies the collapse parameter of the perturbation slowing down the collapse
Test of ID carbon-carbon composite prototype tiles for the SPIDER diagnostic calorimeter
Additional heating will be provided to the thermonuclear fusion experiment ITER by injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction at Consorzio RFX in Padova (Italy), the production of negative ions will be studied and optimised. To this purpose the STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) diagnostic will be used to characterise the SPIDER beam during short operation (several seconds) and to verify if the beam meets the ITER requirement regarding the maximum allowed beam non-uniformity (below \ub110%). The most important measurements performed by STRIKE are beam uniformity, beamlet divergence and stripping losses. The major components of STRIKE are 16 1D-CFC (Carbon matrix-Carbon Fibre reinforced Composite) tiles, observed at the rear side by a thermal camera. The requirements of the 1D CFC material include a large thermal conductivity along the tile thickness (at least 10 times larger than in the other directions); low specific heat and density; uniform parameters over the tile surface; capability to withstand localised heat loads resulting in steep temperature gradients. So 1D CFC is a very anisotropic and delicate material, not commercially available, and prototypes are being specifically realised. This contribution gives an overview of the tests performed on the CFC prototype tiles, aimed at verifying their thermal behaviour. The spatial uniformity of the parameters and the ratio between the thermal conductivities are assessed by means of a power laser at Consorzio RFX. Dedicated linear and non-linear simulations are carried out to interpret the experiments and to estimate the thermal conductivities; these simulations are described and a comparison of the experimental data with the simulation results is presented
Evolution of the Mass-Metallicity relations in passive and star-forming galaxies from SPH-cosmological simulations
We present results from SPH-cosmological simulations, including
self-consistent modelling of SN feedback and chemical evolution, of galaxies
belonging to two clusters and twelve groups. We reproduce the mass-metallicity
(ZM) relation of galaxies classified in two samples according to their
star-forming activity, as parametrized by their sSFR, across a redshift range
up to z=2.
Its slope shows irrelevant evolution in the passive sample, being steeper in
groups than in clusters. However, the sub-sample of high-mass passive galaxies
only is characterized by a steep increase of the slope with redshift, from
which it can be inferred that the bulk of the slope evolution of the ZM
relation is driven by the more massive passive objects. (...ABRIDGED...)
The ZM relation for the star-forming sample reveals an increasing scatter
with redshift, indicating that it is still being built at early epochs. The
star-forming galaxies make up a tight sequence in the SFR-M_* plane at high
redshift, whose scatter increases with time alongside with the consolidation of
the passive sequence. We also confirm the anti-correlation between sSFR and
stellar mass, pointing at a key role of the former in determining the galaxy
downsizing, as the most significant means of diagnostics of the star formation
efficiency. Likewise, an anti-correlation between sSFR and metallicity can be
established for the star-forming galaxies, while on the contrary more active
galaxies in terms of simple SFR are also metal-richer.
We discuss these results in terms of the mechanisms driving the evolution
within the high- and low-mass regimes at different epochs: mergers,
feedback-driven outflows and the intrinsic variation of the star formation
efficiency.Comment: Emended list of author
Stellar population gradients from cosmological simulations: dependence on mass and environment in local galaxies
The age and metallicity gradients for a sample of group and cluster galaxies
from N-body+hydrodynamical simulation are analyzed in terms of galaxy stellar
mass. Dwarf galaxies show null age gradient with a tail of high and positive
values for systems in groups and cluster outskirts. Massive systems have
generally zero age gradients which turn to positive for the most massive ones.
Metallicity gradients are distributed around zero in dwarf galaxies and become
more negative with mass; massive galaxies have steeper negative metallicity
gradients, but the trend flatten with mass. In particular, fossil groups are
characterized by a tighter distribution of both age and metallicity gradients.
We find a good agreement with both local observations and independent
simulations. The results are also discussed in terms of the central age and
metallicity, as well as the total colour, specific star formation and velocity
dispersion.Comment: 9 pages, 5 figures, accepted for publication on MNRA
A study on the multicolour evolution of Red Sequence galaxy populations: insights from hydrodynamical simulations and semi-analytical models
By means of our own cosmological-hydrodynamical simulation and
semi-analytical model we studied galaxy population properties in clusters and
groups, spanning over 10 different bands from UV to NIR, and their evolution
since redshift z=2. We compare our results in terms of galaxy red/blue
fractions and luminous-to-faint ratio (LFR) on the Red Sequence (RS) with
recent observational data reaching beyond z=1.5. Different selection criteria
were tested in order to retrieve galaxies belonging to the RS: either by their
quiescence degree measured from their specific SFR ("Dead Sequence"), or by
their position in a colour-colour plane which is also a function of sSFR. In
both cases, the colour cut and the limiting magnitude threshold were let
evolving with redshift, in order to follow the natural shift of the
characteristic luminosity in the LF.
We find that the Butcher-Oemler effect is wavelength-dependent, with the
fraction of blue galaxies increasing steeper in optical colours than in NIR.
Besides, only when applying a lower limit in terms of fixed absolute magnitude,
a steep BO effect can be reproduced, while the blue fraction results less
evolving when selecting samples by stellar mass or an evolving magnitude limit.
We then find that also the RS-LFR behaviour, highly debated in the literature,
is strongly dependent on the galaxy selection function: in particular its very
mild evolution recovered when measured in terms of stellar mass, is in
agreement with values reported for some of the highest redshift confirmed
(proto)clusters. As to differences through environments, we find that normal
groups and (to a lesser extent) cluster outskirts present the highest values of
both star forming fraction and LFR at low z, while fossil groups and cluster
cores the lowest: this separation among groups begins after z~0.5, while
earlier all group star forming properties are undistinguishable.Comment: revised version, A&A accepted (11 pages, 6 figures
Comptonization of the cosmic microwave background by high energy particles residing in AGN cocoons
X-ray cavities and extended radio sources (`cocoons') surrounding active
galactic nuclei (AGN) have been detected by the Chandra X-ray mission and radio
interferometers. A joint analysis of X-ray and radio maps suggests that
pressure values of non-thermal radio-emitting particles derived from the radio
maps are not sufficient to inflate the X-ray cavities. We propose using the
Sunyaev-Zel'dovich (SZ) effect, whose intensity strongly depends on the
pressure, to find the hitherto undetected, dynamically-dominant component in
the radio cocoons.
We demonstrate that the spectral function at a frequency of 217 GHz has an
absolute maximum at a temperature higher than K, therefore the
measurement of the SZ effect at this frequency is a powerful tool for
potentially revealing the dynamically-dominant component inside AGN jet-driven
radio cocoons. A new method is proposed for excluding the contribution from the
low energy, non-relativistic electrons to the SZ effect by means of
observations at two frequencies. We show how one may correct for a possible
contribution from the kinematic SZ effect. The intensity maps of the SZ effect
are calculated for the self-similar Sedov solution, and application of a
predicted ring-like structure on the SZ map at a frequency of 217 GHz is
proposed to determine the energy released during the active jet stage. The SZ
intensity map for an AGN cocoon in a distant elliptical is calculated using a
2-D numerical simulation and including relativistic corrections to the SZ
effect. We show the intensity spectrum of the SZ effect is flat at high
frequencies if gas temperature is as high as
keV.Comment: 12 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Simulating galaxy clusters -- I. Thermal and chemical properties of the intra-cluster medium
We have performed a series of N-body/hydrodynamical (TreeSPH) simulations of
clusters and groups of galaxies, selected from cosmological N-body simulations
within a CDM framework: these objects have been re-simulated at higher
resolution to =0, in order to follow also the dynamical, thermal and
chemical input on to the ICM from stellar populations within galaxies. The
simulations include metal dependent radiative cooling, star formation according
to different IMFs, energy feedback as strong starburst-driven galactic
super-winds, chemical evolution with non-instantaneous recycling of gas and
heavy elements, effects of a meta-galactic UV field and thermal conduction in
the ICM. In this Paper I of a series of three, we derive results, mainly at
, on the temperature and entropy profiles of the ICM, its X-ray
luminosity, the cluster cold components (cold fraction as well as
mass--to--light ratio) and the metal distribution between ICM and stars.
In general, models with efficient super-winds, along with a top-heavy stellar
IMF, are able to reproduce fairly well the observed relation, the
entropy profiles and the cold fraction. Observed radial ICM temperature
profiles can be matched, except for the gradual decline in temperature inside
of ~0.1. Metal enrichment of the ICM gives rise to
somewhat steep inner iron gradients; yet, the global level of enrichment
compares well to observational estimates after correcting for the stars formed
at late times at the base of the cooling flows; also the metal partition
between stars and ICM gets into good agreement with observations.Comment: 23 pages, 20 colour figures; final version accepte
Laboratory implementation of edge illumination X-ray phase-contrast imaging with energy-resolved detectors
Edge illumination (EI) X-ray phase-contrast imaging (XPCI) has potential for applications in different fields of research, including materials science, non-destructive industrial testing, small-animal imaging, and medical imaging. One of its main advantages is the compatibility with laboratory equipment, in particular with conventional non-microfocal sources, which makes its exploitation in normal research laboratories possible. In this work, we demonstrate that the signal in laboratory implementations of EI can be correctly described with the use of the simplified geometrical optics. Besides enabling the derivation of simple expressions for the sensitivity and spatial resolution of a given EI setup, this model also highlights the EIâs achromaticity. With the aim of improving image quality, as well as to take advantage of the fact that all energies in the spectrum contribute to the image contrast, we carried out EI acquisitions using a photon-counting energy-resolved detector. The obtained results demonstrate that this approach has great potential for future laboratory implementations of EI. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
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