613 research outputs found
Serendipitous discovery of an extended X-ray jet without a radio counterpart in a high-redshift quasar
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led
to the discovery of an extended X-ray jet associated with the high-redshift
background quasar B3 0727+409, a luminous radio source at redshift z=2.5. This
is one of only few examples of high-redshift X-ray jets known to date. It has a
clear extension of about 12", corresponding to a projected length of ~100 kpc,
with a possible hot spot located 35" from the quasar. The archival high
resolution VLA maps surprisingly reveal no extended jet emission, except for
one knot about 1.4" from the quasar. The high X-ray to radio luminosity ratio
for this source appears consistent with the amplification
expected from the inverse Compton radiative model. This serendipitous discovery
may signal the existence of an entire population of similar systems with bright
X-ray and faint radio jets at high redshift, a selection bias which must be
accounted for when drawing any conclusions about the redshift evolution of jet
properties and indeed about the cosmological evolution of supermassive black
holes and active galactic nuclei in general
Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky
We present the results of a very deep (500 ks) Chandra observation, along with tailored numerical simulations, of the nearest, best resolved cluster cold front in the sky, which lies 90 kpc (19 arcmin) to the north-west of M 87. The northern part of the front appears the sharpest, with a width smaller than 2.5 kpc (1.5 Coulomb mean free paths; at 99 per cent confidence). Everywhere along the front, the temperature discontinuity is narrower than 4–8 kpc and the metallicity gradient is narrower than 6 kpc, indicating that diffusion, conduction and mixing are suppressed across the interface. Such transport processes can be naturally suppressed by magnetic fields aligned with the cold front. Interestingly, comparison to magnetohydrodynamic simulations indicates that in order to maintain the observed sharp density and temperature discontinuities, conduction must also be suppressed along the magnetic field lines. However, the northwestern part of the cold front is observed to have a non-zero width. While other explanations are possible, the broadening is consistent with the presence of Kelvin–Helmholtz instabilities (KHI) on length-scales of a few kpc. Based on comparison with simulations, the presence of KHI would imply that the effective viscosity of the intracluster medium is suppressed by more than an order of magnitude with respect to the isotropic Spitzer-like temperature dependent viscosity. Underneath the cold front, we observe quasi-linear features that are ∼10 per cent brighter than the surrounding gas and are separated by ∼15 kpc from each other in projection. Comparison to tailored numerical simulations suggests that the observed phenomena may be due to the amplification of magnetic fields by gas sloshing in wide layers below the cold front, where the magnetic pressure reaches ∼5–10 per cent of the thermal pressure, reducing the gas density between the bright features
Substructures in the core of Abell 2319
We analysed the deep archival Chandra observations of the high-temperature
galaxy cluster Abell 2319 to investigate the prominent cold front in its core.
The main sharp arc of the front shows wiggles, or variations of the radius of
the density jump along the arc. At the southern end of the arc is a feature
that resembles a Kelvin-Helmholtz (KH) eddy, beyond which the sharp front
dissolves. These features suggest that KH instabilities develop at the front.
Under this assumption, we can place an upper limit on the ICM viscosity that is
several times below the isotropic Spitzer value. Other features include a split
of the cold front at its northern edge, which may be another KH eddy. There is
a small pocket of hot, less-dense gas inside the cold front, which may indicate
a `hole' in the front's magnetic insulation layer that lets the heat from the
outer gas to penetrate inside the front. Finally, a large concave brightness
feature southwest of the cluster core can be caused by the gasdynamic
instabilities. We speculate that it can also be an inner boundary of a giant
AGN bubble, similar to that in Ophiuchus. If the latter interpretation is
supported by better radio data, this could be a remnant of another extremely
powerful AGN outburst.Comment: Accepted for publication in MNRA
Gas Density Perturbations in Cool Cores of CLASH Galaxy Clusters
We present a systematic study of gas density perturbations in cool cores of
high-mass galaxy clusters. We select 12 relaxed clusters from the Cluster
Lensing And Supernova survey with Hubble (CLASH) sample and analyze their cool
core features observed with the Chandra X-ray Observatory. We focus on the
X-ray residual image characteristics after subtracting their global profile of
the X-ray surface brightness distribution. We find that all the galaxy clusters
in our sample have, at least, both one positive and one negative excess regions
in the X-ray residual image, indicating the presence of gas density
perturbations. We identify and characterize the locally perturbed regions using
our detection algorithm, and extract X-ray spectra of the intracluster medium
(ICM). The ICM temperature in the positive excess region is lower than that in
the negative excess region, whereas the ICM in both regions is in pressure
equilibrium in a systematic manner. These results indicate that gas sloshing in
cool cores takes place in more than 80% of relaxed clusters (95% CL). We
confirm this physical picture by analyzing synthetic X-ray observations of a
cool-core cluster from a hydrodynamic simulation, finding that our detection
algorithm can accurately extract both the positive and negative excess regions
and can reproduce the temperature difference between them. Our findings support
the picture that the gas density perturbations are induced by gas sloshing, and
a large fraction of cool-core clusters have undergone gas sloshing, indicating
that gas sloshing may be capable of suppressing runaway cooling of the ICM.Comment: 30 pages, 8 figures, accepted for publication in Ap
Cortical representation area of human dental pulp
博士(歯学)・第1662号(甲第958号)・平成18年3月31
Human annexin A6 interacts with influenza a virus protein M2 and negatively modulates infection
Copyright © 2012, American Society for Microbiology. All Rights ReservedThe influenza A virus M2 ion channel protein has the longest cytoplasmic tail (CT) among the three viral envelope proteins and is well conserved between different viral strains. It is accessible to the host cellular machinery after fusion with the endosomal membrane and during the trafficking, assembly, and budding processes. We hypothesized that identification of host cellular interactants of M2 CT could help us to better understand the molecular mechanisms regulating the M2-dependent stages of the virus life cycle. Using yeast two-hybrid screening with M2 CT as bait, a novel interaction with the human annexin A6 (AnxA6) protein was identified, and their physical interaction was confirmed by coimmunoprecipitation assay and a colocalization study of virus-infected human cells. We found that small interfering RNA (siRNA)-mediated knockdown of AnxA6 expression significantly increased virus production, while its overexpression could reduce the titer of virus progeny, suggesting a negative regulatory role for AnxA6 during influenza A virus infection. Further characterization revealed that AnxA6 depletion or overexpression had no effect on the early stages of the virus life cycle or on viral RNA replication but impaired the release of progeny virus, as suggested by delayed or defective budding events observed at the plasma membrane of virus-infected cells by transmission electron microscopy. Collectively, this work identifies AnxA6 as a novel cellular regulator that targets and impairs the virus budding and release stages of the influenza A virus life cycle.This work was supported by the Research Fund for the Control of Infectious Disease (project 09080892) of the Hong Kong Government, the Area of Excellence Scheme of the University Grants Committee (grant
AoE/M-12/-06 of the Hong Kong Special Administrative Region, China), the French Ministry of Health, the RESPARI Pasteur Network
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