573 research outputs found
An X-ray/optical study of the complex dynamics of the core of the massive intermediate-redshift cluster MACSJ0717.5+3745
Using CHANDRA, we investigate the spatial temperature distribution of the
intracluster medium (ICM) within 700 kpc of the center of the massive merging
cluster MACSJ0717.5+3745 at z=0.55. Combining the X-ray evidence with
information about the distribution and velocities of the cluster galaxies near
the core provides us with a snapshot of the three-dimensional geometry and
dynamics of one of the most complex cluster studied to date. We find
MACSJ0717.5+3745 to be an active triple merger with ICM temperatures exceeding
20 keV. Although radial velocity information and X-ray/optical offsets indicate
that all three mergers proceed along distinctly different directions, the
partial alignment of the merger axes points to a common origin in the
large-scale filament south-east of the cluster core. Clear decrements in the
ICM temperature observed near two of these subclusters identify the respective
X-ray surface brightness peaks as remnants of cool cores; the compactness and
low temperature of 5.7 keV of one of these features suggest that the respective
merger, a high-velocity collision at 3,000 km/s, is still in its very early
stages. Looking beyond the triple merger, we find the large-scale filament to
not only provide a spatial as well as temporal arrow for the interpretation of
the dynamics of the merger events near the cluster core; we also find
tantalizing, if circumstantial, evidence for direct, large-scale heating of the
ICM by contiguous infall of low-density gas from the filament.Comment: accepted by ApJL, 2 color figures, fix the typo of one author's nam
The three-dimensional geometry and merger history of the massive galaxy cluster MACS J0358.8-2955
We present results of a combined X-ray/optical analysis of the dynamics of
the massive cluster MACS J0358.8-2955 (z=0.428) based on observations with the
Chandra X-ray Observatory, the Hubble Space Telescope, and the Keck-I telescope
on Mauna Kea. MACS J0358.8-2955 is found to be one of the most X-ray luminous
clusters known at z>0.3, featuring L_X(<r_500) = 4.24*10^45 erg/s, kT = (9.55
+0.58/-0.37) keV, M^{3D}_{gas}(<r_500) = (9.18+/-1.45)*10^13 M_sun, and
M^{3D}_{tot}(<r_500) = (1.12+/-0.18)*10^15 M_sun. The system's high velocity
dispersion of (1440 +130/-110) km/s (890 km/s when the correct relativistic
equation is used), however, is inflated by infall along the line of sight, as
the result of a complex merger of at least three sub-clusters. One collision
proceeds close to head-on, while the second features a significant impact
parameter. The temperature variations in the intra-cluster gas, two tentative
cold fronts, the radial velocities measured for cluster galaxies, and the small
offsets between collisional and non-collisional cluster components all suggest
that both merger events are observed close to core passage and along axes that
are greatly inclined with respect to the plane of the sky. A strong-lensing
analysis of the system anchored upon three triple-image systems (two of which
have spectroscopic redshifts) yields independent constraints on the mass
distribution. For a gas fraction of 8.2%, the resulting strong-lensing mass
profile is in good agreement with our X-ray estimates, and the details of the
mass distribution are fully consistent with our interpretation of the
three-dimensional merger history of this complex system.Comment: 17 pages, 17 figures, and 4 tables. Accepted for publication in MNRA
Statistical Properties of Supercluster-Like Filaments from Cosmological Simulations
We study large-scale structures from numerical simulations, paying particular
attention to supercluster-like structures. A grid-density-contour based
algorithm is adopted to locate connected groups. With the increase of the
linking density threshold, the foam- like cosmic web is subsequently broken
into individual supercluster-like groups and further halos which are in
accordance to groups with the linking density threshold {\rho}/{\rho}= 1 +
{\delta} = 80. By analyzing sets of cosmological simulations with varying
cosmological parameters, we find that an universal mass function exists not
only for halos but also for low-density supercluster-like groups until the
linking density threshold decreases to a density where the global percolation
of large-scale structures occurs. We further show that the mass functions of
different groups can be well described by the Jenkins form with the parameters
being dependent on the linking density threshold. On the other hand, these low-
density supercluster-like groups cannot be directly associated with the
predictions from the excursion set theory with effective barriers obtained from
dynamical collapse models, and the peak exclusion effect must be taken into
account. Including such an effect, the mass function of groups with the linking
density threshold 1 + {\delta} = 16 is in good agreements with that from the
excursion set theory with a nearly flat effective barrier. A simplified
analysis of the ellipsoidal collapse model indicates that the barrier for
collapses along two axes to form filaments is approximately flat in scales,
thus we define groups identified with 1 + {\delta} = 16 as filaments. We then
further study the halo-filament conditional mass function and the filament-halo
conditional mass function, and compare them with the predictions from the
two-barrier excursion set theory. The shape statistics for filaments are also
presented.Comment: Accepted by Ap
The impact of a major cluster merger on galaxy evolution in MACS\,J0025.4-1225
We present results of an extensive morphological, spectroscopic, and
photometric study of the galaxy population of MACS J0025.41225 (z=0.586), a
major cluster merger with clear segregation of dark and luminous matter, to
examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra
obtained with Keck DEIMOS, we identified 212 cluster members within 4 Mpc of
the cluster centre, and classified them using three spectroscopic types; we
find 111 absorption-line, 90 emission-line (including 23 e(a) and 11 e(b)), and
6 E+A galaxies. The fraction of absorption(emission)-line galaxies is a
monotonically increasing(decreasing) function of both projected galaxy density
and radial distance to the cluster center. More importantly, the 6 observed E+A
cluster members are all located between the dark-matter peaks of the cluster
and within ~0.3Mpc radius of the X-ray flux peak, unlike the E+A galaxies in
other intermediate-redshift clusters which are usually found to avoid the core
region. In addition, we use Hubble Space Telescope imaging to classify cluster
members according to morphological type. We find the global fraction of spiral
and lenticular galaxies in MACS J0025 to be among the highest observed to date
in clusters at z>0.5. The observed E+A galaxies are found to be of lenticular
type with Sersic indices of ~2, boosting the local fraction of S0 to 70 per
cent between the dark-matter peaks. Combing the results of our analysis of the
spatial distribution, morphology, and spectroscopic features of the galaxy
population, we propose that the starburst phase of these E+A galaxies was both
initiated and terminated during the first core-passage about 0.5--1Gyr ago, and
that their morphology has already been transformed into S0 due to ram pressure
and/or tidal forces near the cluster core. By contrast, ongoing starbursts are
observed predominantly in infalling galaxies, and thus appears to be unrelated
to the cluster merger.Comment: 18 pages, 17 figures, accepted by MNRA
Halo mass - concentration relation from weak lensing
We perform a statistical weak lensing analysis of dark matter profiles around
tracers of halo mass from galactic- to cluster-size halos. In this analysis we
use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236
groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823
MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range
of richness. Together these three samples allow a determination of the density
profiles of dark matter halos over three orders of magnitude in mass, from
10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent
with an NFW or Einasto profile on scales outside the central region. We find
that the NFW concentration parameter c_{200b} decreases with halo mass, from
around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on
halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find
c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results
for the Einasto profile. The slope (\beta) is in agreement with theoretical
predictions, while the amplitude is about two standard deviations below the
predictions for this mass and redshift, but we note that the published values
in the literature differ at a level of 10-20% and that for a proper comparison
our analysis should be repeated in simulations. We discuss the implications of
our results for the baryonic effects on the shear power spectrum: since these
are expected to increase the halo concentration, the fact that we see no
evidence of high concentrations on scales above 20% of the virial radius
suggests that baryonic effects are limited to small scales, and are not a
significant source of uncertainty for the current weak lensing measurements of
the dark matter power spectrum. [ABRIDGED]Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that
are included in v2 here on arXi
Steroid-refractory ulcerative colitis treated with corticosteroids, metronidazole and vancomycin: a case report
BACKGROUND: Increasing evidence elucidating the pathogenic mechanisms of ulcerative colitis (UC) has accumulated and the disease is widely assumed to be the consequence of genetic susceptibility and an abnormal immune response to commensal bacteria. However evidence regarding an infectious etiology in UC remains elusive. CASE PRESENTATION: We report a provocative case of UC with profound rheumatologic involvement directly preceded by Clostridium difficile infection and accompanying fever, vomiting, bloody diarrhea, and arthritis. Colonic biopsy revealed a histopathology suggestive of UC. Antibiotic treatment eliminated detectable levels of enteric pathogens but did not abate symptoms. Resolution of symptoms was procurable with oral prednisone, but tapering of corticosteroids was only achievable in combination therapy with vancomycin and metronidazole. CONCLUSIONS: An infectious pathogen may have both precipitated and exacerbated autoimmune disease attributes in UC, symptoms of which could be resolved only with a combination of corticosteroids, vancomycin and metronidazole. This may warrant the need for more perceptive scrutiny of C. difficile and the like in patients with UC
MUC1 Limits Helicobacter pylori Infection both by Steric Hindrance and by Acting as a Releasable Decoy
The bacterium Helicobacter pylori can cause peptic ulcer disease, gastric adenocarcinoma and MALT lymphoma. The cell-surface mucin MUC1 is a large glycoprotein which is highly expressed on the mucosal surface and limits the density of H. pylori in a murine infection model. We now demonstrate that by using the BabA and SabA adhesins, H. pylori bind MUC1 isolated from human gastric cells and MUC1 shed into gastric juice. Both H. pylori carrying these adhesins, and beads coated with MUC1 antibodies, induced shedding of MUC1 from MKN7 human gastric epithelial cells, and shed MUC1 was found bound to H. pylori. Shedding of MUC1 from non-infected cells was not mediated by the known MUC1 sheddases ADAM17 and MMP-14. However, knockdown of MMP-14 partially affected MUC1 release early in infection, whereas ADAM17 had no effect. Thus, it is likely that shedding is mediated both by proteases and by disassociation of the non-covalent interaction between the α- and β-subunits. H. pylori bound more readily to MUC1 depleted cells even when the bacteria lacked the BabA and SabA adhesins, showing that MUC1 inhibits attachment even when bacteria cannot bind to the mucin. Bacteria lacking both the BabA and SabA adhesins caused less apoptosis in MKN7 cells than wild-type bacteria, having a greater effect than deletion of the CagA pathogenicity gene. Deficiency of MUC1/Muc1 resulted in increased epithelial cell apoptosis, both in MKN7 cells in vitro, and in H. pylori infected mice. Thus, MUC1 protects the epithelium from non-MUC1 binding bacteria by inhibiting adhesion to the cell surface by steric hindrance, and from MUC1-binding bacteria by acting as a releasable decoy
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