763 research outputs found
Shock heating of the merging galaxy cluster A521
A521 is an interacting galaxy cluster located at z=0.247, hosting a low
frequency radio halo connected to an eastern radio relic. Previous Chandra
observations hinted at the presence of an X-ray brightness edge at the position
of the relic, which may be a shock front. We analyze a deep observation of A521
recently performed with XMM-Newton in order to probe the cluster structure up
to the outermost regions covered by the radio emission. The cluster atmosphere
exhibits various brightness and temperature anisotropies. In particular, two
cluster cores appear to be separated by two cold fronts. We find two shock
fronts, one that was suggested by Chandra and that is propagating to the east,
and another to the southwestern cluster outskirt. The two main interacting
clusters appear to be separated by a shock heated region, which exhibits a
spatial correlation with the radio halo. The outer edge of the radio relic
coincides spatially with a shock front, suggesting this shock is responsible
for the generation of cosmic ray electrons in the relic. The propagation
direction and Mach number of the shock front derived from the gas density jump,
M = 2.4 +/- 0.2, are consistent with expectations from the radio spectral
index, under the assumption of Fermi I acceleration mechanism
The effect of renovation of long-term temperate grassland on N2O emissions and N leaching from contrasting soils
pre-printRenovation of long-term grassland is associated with a peak in soil organic N mineralisation which, coupled with diminished plant N uptake can lead to large gaseous and leaching N losses. This study reports on the effect of ploughing and subsequent N fertilisation on the N2O emissions and DON/NO3â leaching, and evaluates the impact of ploughing technique on the magnitude and profile of N losses. This study was carried out on isolated grassland lysimeters of three Irish soils representing contrasting drainage properties (well-drained Clonakilty, moderately-drained Elton and poorly-drained Rathangan). Lysimeters were manually ploughed simulating conventional (CT) and minimum tillage (MT) as two treatments. Renovation of grassland increased N2O flux to a maximum of 0.9 kg N2OâN haâ 1 from poorly-drained soil over four days after treatment. Although there was no difference between CT and MT in the post-ploughing period, the treatment influenced subsequent N2O after fertiliser applications. Fertilisation remained the major driver of N losses therefore reducing fertilisation rate post-planting to account for N mineralised through grassland renovation could reduce the losses in medium to longer term. Leaching was a significant loss pathway, with the cumulative drainage volume and N leached highly influenced by soil type. Overall, the total N losses (N2O + N leached) were lowest from poorly and moderately draining soil and highest for the well draining soil, reflecting the dominance of leaching on total N losses and the paramount importance of soil properties
Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster
We present two new examples of galaxies undergoing transformation in the
Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10
Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and
SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in
ugriK bands and in Halpha narrow-band are used to disentangle the effects of
tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies,
SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending
respectively 30kpc and 41kpc in projection from their disks. The galaxies'
gaseous disks are truncated and the kinematics of the stellar and gas
components are decoupled, supporting the RPS scenario. The emission of the
ionized gas extends in the direction of a possible companion for both galaxies
suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by
ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and
starting about 250Myr ago, consistent with the age of the young stellar
populations. A link between the observed gas stripping and the cluster-cluster
interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of
ram pressure acting almost edge-on are able to fully reproduce the gas velocity
field of SOS-90630, but cannot at the same time reproduce the extended tail of
outflowing gas. This suggests that an additional disturbance from a TI is
required. This study adds a piece of evidence that RPS may take place in
different environments with different impacts and witnesses the possible effect
of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte
A2163: Merger events in the hottest Abell galaxy cluster II. Subcluster accretion with galaxy-gas separation
Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster
medium (ICM) that exhibits extraordinary properties, including an exceptionally
high X-ray luminosity, average temperature, and a powerful and extended radio
halo. The irregular and complex morphology of its gas and galaxy structure
suggests that this cluster has recently undergone major merger events that
involve two or more cluster components. In this paper, we study the gas
structure and dynamics by means of spectral-imaging analysis of X-ray data
obtained from XMM-Newton and Chandra observations. From the evidence of a cold
front, we infer the westward motion of a cool core across the E-W elongated
atmosphere of the main cluster A2163-A. Located close to a galaxy over-density,
this gas 'bullet' appears to have been spatially separated from its galaxy (and
presumably dark matter component) as a result of high-velocity accretion.
From gas brightness and temperature profile analysis performed in two
opposite regions of the main cluster, we show that the ICM has been
adiabatically compressed behind the crossing 'bullet' possibly because of shock
heating, leading to a strong departure of the ICM from hydrostatic equilibrium
in this region. Assuming that the mass estimated from the Yx proxy best
indicates the overall mass of the system and that the western cluster sector is
in approximate hydrostatic equilibrium before subcluster accretion, we infer a
merger scenario between two subunits of mass ratio 1:4, leading to a present
total system mass of M500 . The exceptional
properties of A2163 present various similarities with those of 1E0657-56, the
so-called 'bullet-cluster'. These similarities are likely to be related to a
comparable merger scenario.Comment: A&A, in pres
Stress fluctuation, crack renucleation and toughening in layered materials
It has been established that contrast in the elastic properties can lead to enhancement of fracture toughness in heterogeneous materials. Focussing on layered materials as a model system, we show that this enhancement is a result of two distinct phenomena â first, fluctuations in stress leading to regions where the stress intensity at the crack is considerably smaller than that of the macroscopically applied value; and second, the lack of stress intensity when a crack is at a compliant to stiff interface thereby requiring renucleation. Using theoretical, computational and experimental methods, we study two geometries â a layered material and a layered material with a narrow channel â to separate the two phenomena. The stress fluctuation is present in both, but renucleation is present only in the layered medium. We provide quantitative estimates for the enhanced toughness
Etat immunitaire actuel, naturel ou acquis du cheptel sénégalais vis-à -vis de la peste bovine, de la maladie des muqueuses, de la rhinotrachéite infectieuse et de la maladie respiratoire à virus Parainfluenza III
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Application de la méthode de séroneutralisation cinétique à la recherche des anticorps neutralisant le virus de la peste bovine chez les bovins, les caprins et les ovins
La mĂ©thode cinĂ©tique de sĂ©ro-neutralisation mise au point par LEPINE, ROGER et ROGER (1959) peut ĂȘtre adaptĂ©e avec quelques modifications Ă la recherche des anticorps bovipestiques chez les bovins, les ovins et les caprins. Elle a rĂ©vĂ©lĂ©, au SĂ©nĂ©gal, que 48 p. 100 des caprins et 62,7 p. 100 des ovins vivant en zone d'endĂ©mie Ă©taient porteurs d'anticorps neutralisants, ce chiffre descendant Ă 28 p. 100 pour les caprins vivant en zone indemne. La responsabilitĂ© de la prĂ©sence de ces anticorps en zone indemne peut ĂȘtre attribuĂ©e au virus PP
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