620 research outputs found
Properties of gas clumps and gas clumping factor in the intra cluster medium
The spatial distribution of gas matter inside galaxy clusters is not
completely smooth, but may host gas clumps associated with substructures. These
overdense gas substructures are generally a source of unresolved bias of X-ray
observations towards high density gas, but their bright luminosity peaks may be
resolved sources within the ICM, that deep X-ray exposures may be (already)
capable to detect. In this paper we aim at investigating both features, using a
set of high-resolution cosmological simulations with ENZO. First, we monitor
how the bias by unresolved gas clumping may yield incorrect estimates of global
cluster parameters and affects the measurements of baryon fractions by X-ray
observations. We find that based on X-ray observations of narrow radial strips,
it is difficult to recover the real baryon fraction to better than 10 - 20
percent uncertainty. Second, we investigated the possibility of observing
bright X-ray clumps in the nearby Universe (z<=0.3). We produced simple mock
X-ray observations for several instruments (XMM, Suzaku and ROSAT) and
extracted the statistics of potentially detectable bright clumps. Some of the
brightest clumps predicted by simulations may already have been already
detected in X- ray images with a large field of view. However, their small
projected size makes it difficult to prove their existence based on X-ray
morphology only. Preheating, AGN feedback and cosmic rays are found to have
little impact on the statistical properties of gas clumps.Comment: 17 pages, 11 figures. MNRAS accepte
On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C +67.13
Here we analyze radio, optical, and X-ray data for a peculiar cluster Abell
578. This cluster is not fully relaxed and consists of two merging sub-systems.
The brightest cluster galaxy, CGPG 0719.8+6704, is a pair of interacting
ellipticals with projected separation 10 kpc, the brighter of which hosts
the radio source 4C +67.13. The Fanaroff-Riley type-II radio morphology of 4C
+67.13 is unusual for central radio galaxies in local Abell clusters. Our new
optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are
active, albeit at low accretion rates corresponding to the Eddington ratio
(for the estimated black hole masses of and ). The gathered X-ray ({\it Chandra})
data allowed us to confirm and to quantify robustly the previously noted
elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a
large spatial offset (\,kpc projected) between the position of the
brightest cluster galaxy and the cluster center inferred from the modeling of
the X-ray surface brightness distribution. Detailed analysis of the brightness
profiles and temperature revealed also that the cluster gas in the vicinity of
4C\,+67.13 is compressed (by a factor of about ) and heated (from
\,keV up to 2.7\,keV), consistent with the presence of a weak shock
(Mach number ) driven by the expanding jet cocoon. This would then
require the jet kinetic power of the order of \,erg\,s,
implying either a very high efficiency of the jet production for the current
accretion rate, or a highly modulated jet/accretion activity in the system.Comment: 12 pages, 11 figures, accepted for publication in Ap
On the Interaction of the PKS B1358-113 Radio Galaxy with the Abell 1836 Cluster
[abridged] Here we present the analysis of multifrequency data gathered for
the FRII radio galaxy PKS B1358-113, hosted in the brightest cluster galaxy of
Abell 1836. The galaxy harbors one of the most massive black holes known to
date and our analysis of the optical data reveals that this black hole is only
weakly active. Based on new Chandra and XMM-Newton X-ray observations and
archival radio data we derive the preferred range for the jet kinetic
luminosity erg s. This is above the values
implied by various scaling relations proposed for radio sources in galaxy
clusters, being instead very close to the maximum jet power allowed for the
given accretion rate. We constrain the radio source lifetime as
Myrs, and the total amount of deposited jet energy \,ergs. The detailed analysis of the X-ray data provides indication for
the presence of a bow-shock driven by the expanding radio lobes into the Abell
1836 cluster environment, with the corresponding Mach number . This,
together with the recently growing evidence that powerful FRII radio galaxies
may not be uncommon in the centers of clusters at higher redshifts, supports
the idea that jet-induced shock heating may indeed play an important role in
shaping the properties of clusters, galaxy groups, and galaxies in formation.
We speculate on a possible bias against detecting jet-driven shocks in poorer
environments, resulting from an inefficient electron heating at the shock
front, combined with a relatively long electron-ion equilibration timescale.Comment: Version accepted to Ap
Metal transport by gas sloshing in M87
We present the results of an XMM-Newton mosaic covering the central ~200 kpc
of the nearby Virgo cluster. We focus on a strong surface brightness
discontinuity in the outskirts of the brightest cluster galaxy, M87. Using both
XMM-Newton and Suzaku, we derive accurate temperature and metallicity profiles
across this feature and show that it is a cold front probably due to sloshing
of the Virgo ICM. It is also associated with a discontinuity in the chemical
composition. The gas in the inner, bright region of the front is ~40% more
abundant in Fe than the gas outside the front, suggesting the important role of
sloshing in transporting metals through the ICM. For the first time, we provide
a quantitative estimate of the mass of Fe transported by a cold front. This
amounts to ~6% of the total Fe mass within the radial range affected by
sloshing, significantly more than the amount of metals transported by the AGN
in the same cluster core. The very low Fe abundance of only ~0.2 solar
immediately outside the cold front at a radius of 90 kpc suggests we are
witnessing first-hand the transport of higher metallicity gas into a pristine
region, whose abundance is typical of the cluster outskirts. The Mg/Fe and O/Fe
abundance ratios remain approximately constant over the entire radial range
between the centre of M87 and the faint side of the cold front, which requires
the presence of a centrally peaked distribution not only for Fe but also for
core-collapse type supernova products. This peak may stem from the star
formation triggered as the BCG assembled during the protocluster phase.Comment: accepted for publication in MNRA
The chemical and thermal structure of the hot atmosphere of the elliptical galaxy NGC 5813
Galaxie
Effective Strategic Management - Manager Performance
Managers are a very important component of human resources within an organization, and they make a decisive contribution to establishing and achieving the company's goals.
In the context of the global development of the economy, both the roles and the tasks of the managers of any type of organization have changed; which is why the success of an enterprise / institution / school, etc. depends on the quality of managers.
Exercising a performance management must transform the organization so that it becomes the "ideal employer" in which the employee is enthusiastic and devoted to his work. Through their position and role in organizations, leaders must be able to exercise effective leadership at all levels to make their employees feel valued, productive and listening; to offer opportunities for learning and improving each employee; to create a productive climate that allows the balance between work and personal life to be maintained
Cold gas in the Intra Cluster Medium: implications for flow dynamics and powering optical nebulae
We show that the mechanical energy injection rate generated as the
intra-cluster medium (ICM) flows around cold clouds may be sufficient to power
the optical and near infra-red emission of nebulae observed in the central
regions of a sample of seven galaxy clusters. The energy injection rate is
extremely sensitive to the velocity difference between the ICM and cold clouds,
which may help to explain why optical and infra-red luminosity is often larger
than expected in systems containing AGNs. We also find that mass recycling is
likely to be important for the dynamics of the ICM. This effect will be
strongest in the central regions of clusters where there is more than enough
cold gas for its evaporation to contribute significantly to the density of the
hot phase.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Impact of magnetic fields on ram pressure stripping in disk galaxies
(abridged) Ram pressure can remove significant amounts of gas from galaxies
in clusters, and thus has a large impact on the evolution of cluster galaxies.
Recent observations have shown that key properties of ram pressure stripped
tails of galaxies are in conflict with predictions by simulations. To increase
the realism of existing simulations, we simulated for the first time a disk
galaxy exposed to a uniformly magnetized wind including radiative cooling and
self-gravity of the gas. We find that B-fields have a strong effect on the
morphology of the gas in the tail of the galaxy. While in the pure hydro case
the tail is very clumpy, the MHD case shows very filamentary structures in the
tail. The filaments can be strongly supported by magnetic pressure and, when
this is the case, the B-field vectors tend to be aligned with the filaments.
The ram pressure stripping may lead to the formation of magnetized density
tails that appear as bifurcated in the plane of the sky and resemble the double
tails observed in ESO 137-001 and ESO 137-002. Such tails can be formed under a
variety of situations, both for the disks oriented face-on with respect to the
ICM wind and for the tilted ones. While this bifurcation is due to the generic
tendency for the B-fields to produce very filamentary tail morphology, the tail
properties are further shaped by the combination of the B-field orientation and
the sliding of the field past the disk surface exposed to the wind. Magnetic
draping does not strongly change the rate of gas stripping. For a face-on
galaxy, the field tends to reduce the amount of stripping compared to the pure
hydro case, and is associated with the formation of a magnetic draping layer on
the side of the galaxy exposed to the ICM wind. For significantly tilted disks,
the stripping rate may be enhanced by the ``scraping'' of the disk surface by
the B-fields sliding past the ISM/ICM interface.Comment: ApJ in press. arXiv admin note: text overlap with arXiv:0909.3097 by
other author
- …