4,210 research outputs found
Chandra and XMM-Newton Observations of the Abell 3391/Abell 3395 Intercluster Filament
We present Chandra and XMM-Newton X-ray observations of the Abell 3391/Abell
3395 intercluster filament. It has been suggested that the galaxy clusters
Abell 3395, Abell 3391, and the galaxy group ESO-161 located between the two
clusters, are in alignment along a large-scale intercluster filament. We find
that the filament is aligned close to the plane of the sky, in contrast to
previous results. We find a global projected filament temperature kT =
~keV, electron density ~cm, and ~M. The thermodynamic properties of the filament are consistent
with that of intracluster medium (ICM) of Abell 3395 and Abell 3391, suggesting
that the filament emission is dominated by ICM gas that has been tidally
disrupted during an early stage merger between these two clusters. We present
temperature, density, entropy, and abundance profiles across the filament. We
find that the galaxy group ESO-161 may be undergoing ram pressure stripping in
the low density environment at or near the virial radius of both clusters due
to its rapid motion through the filament.Comment: 13 Pages, 12 Figures, 5 Tables. Submitted to ApJ, comments are
welcom
IL-2 limits IL-12 enhanced lymphocyte proliferation during \u3ci\u3eLeishmania amazonensis\u3c/i\u3e infection
C3H mice infected with Leishmania amazonensis develop persistent, localized lesions with high parasite loads. During infection, memory/effector CD44hiCD4+ T cells proliferate and produce IL-2, but do not polarize to a known effector phenotype. Previous studies have demonstrated IL-12 is insufficient to skew these antigen-responsive T cells to a functional Th1 response. To determine the mechanism of this IL-12 unresponsiveness, we used an in vitro assay of repeated antigen activation. Memory/effector CD44hiCD4+ T cells did not increase proliferation in response to either IL-2 or IL-12, although these cytokines upregulated CD25 expression. Neutralization of IL-2 enhanced CD4+ T cell proliferation in response to IL-12. This cross-regulation of IL-12 responsiveness by IL-2 was confirmed in vivo by treatment with anti-IL-2 antibodies and IL-12 during antigen challenge of previously infected mice. These results suggest that during chronic infection with L. amazonensis, IL-2 plays a dominant, immunosuppressive role independent of identifiable conventional Treg cells
IL-2 limits IL-12 enhanced lymphocyte proliferation during \u3ci\u3eLeishmania amazonensis\u3c/i\u3e infection
C3H mice infected with Leishmania amazonensis develop persistent, localized lesions with high parasite loads. During infection, memory/effector CD44hiCD4+ T cells proliferate and produce IL-2, but do not polarize to a known effector phenotype. Previous studies have demonstrated IL-12 is insufficient to skew these antigen-responsive T cells to a functional Th1 response. To determine the mechanism of this IL-12 unresponsiveness, we used an in vitro assay of repeated antigen activation. Memory/effector CD44hiCD4+ T cells did not increase proliferation in response to either IL-2 or IL-12, although these cytokines upregulated CD25 expression. Neutralization of IL-2 enhanced CD4+ T cell proliferation in response to IL-12. This cross-regulation of IL-12 responsiveness by IL-2 was confirmed in vivo by treatment with anti-IL-2 antibodies and IL-12 during antigen challenge of previously infected mice. These results suggest that during chronic infection with L. amazonensis, IL-2 plays a dominant, immunosuppressive role independent of identifiable conventional Treg cells
Detection of a Star Forming Galaxy in the Center of a Low-Mass Galaxy Cluster
Brightest Cluster Galaxies (BCGs) residing in the centers of galaxy clusters
are typically quenched giant ellipticals. A recent study hinted that
star-forming galaxies with large disks, so-called superluminous spirals and
lenticulars, are the BCGs of a subset of galaxy clusters. Based on the existing
optical data it was not possible to constrain whether the superluminous disk
galaxies reside at the center of galaxy clusters. In this work, we utilize
XMM-Newton X-ray observations of five galaxy clusters to map the morphology of
the intracluster medium (ICM), characterize the galaxy clusters, determine the
position of the cluster center, and measure the offset between the cluster
center and the superluminous disk galaxies. We demonstrate that one
superluminous lenticular galaxy, 2MASX J10405643-0103584, resides at the center
of a low-mass () galaxy cluster. This
represents the first conclusive evidence that a superluminous disk galaxy is
the central BCG of a galaxy cluster. We speculate that the progenitor of 2MASX
J10405643-0103584 was an elliptical galaxy, whose extended disk was re-formed
due to the merger of galaxies. We exclude the possibility that the other four
superluminous disk galaxies reside at the center of galaxy clusters, as their
projected distance from the cluster center is kpc, which corresponds
to . We conclude that these clusters host quiescent
massive elliptical galaxies at their center.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster
Structure formation models predict that clusters of galaxies contain numerous
massive subhalos. The gravity of a subhalo in a cluster compresses the
surrounding intracluster gas and enhances its X-ray emission. We present a
simple model, which treats subhalos as slow moving and gasless, for computing
this effect. Recent weak lensing measurements by Okabe et al. have determined
masses of ~ 10^13 solar masses for three mass concentrations projected within
300 kpc of the center of the Coma Cluster, two of which are centered on the
giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a smooth spheroidal
beta-model for the gas distribution in the unperturbed cluster, we model the
effect of these subhalos on the X-ray morphology of the Coma Cluster, comparing
our results to Chandra and XMM-Newton X-ray data. The agreement between the
models and the X-ray morphology of the central Coma Cluster is striking. With
subhalo parameters from the lensing measurements, the distances of the three
subhalos from the Coma Cluster midplane along our line of sight are all tightly
constrained. Using the model to fit the subhalo masses for NGC 4889 and NGC
4874 gives 9.1 x 10^12 and 7.6 x 10^12 solar masses, respectively, in good
agreement with the lensing masses. These results lend strong support to the
argument that NGC 4889 and NGC 4874 are each associated with a subhalo that
resides near the center of the Coma Cluster. In addition to constraining the
masses and 3-d location of subhalos, the X-ray data show promise as a means of
probing the structure of central subhalos.Comment: ApJ, in press. Matches the published versio
Chandra Observations of NGC 4438: An Environmentally Damaged Galaxy in the Virgo Cluster
We present results from a 25 ksec CHANDRA ACIS-S observation of galaxies
NGC4438 and NGC4435 in the Virgo Cluster. X-ray emission in NGC4438 is observed
in a ~700 pc nuclear region, a 2.3 kpc spherical bulge, and a network of
filaments extending 4-10 kpc to the W and SW of the galaxy. The X-ray emission
in all 3 regions is highly correlated to similar features observed in Halpha.
Spectra of the filaments and bulge are well represented by a 0.4 keV MEKAL
model with combined 0.3-2 keV intrinsic luminosity of 1.24x10^{40}erg/s,
electron densities ~ 0.02-0.04 cm^{-3}, cooling times of 400-700 Myr and X-ray
gas mass <~ 3.7x10^8 Msolar. In the nuclear region of NGC4438 X-ray emission is
seen from the nucleus and from two outflow bubbles extending 360(730) pc to the
NW(SE) of the nucleus. The spectrum of the NW outflow bubble plus nucleus is
well fitted by an absorbed (n_H=1.9x10^{21} cm^{-2}) 0.58 keV MEKAL plasma
model plus a heavily absorbed (n_H = 2.9 x10^{22} cm^{-2}) Gamma = 2, power law
component. The electron density, cooling time, and X-ray gas mass in the NW
outflow are ~0.5 cm^{-3}, 30 Myr and 3.5x10^6 Msolar. Weak X-ray emission is
observed in the central region of NGC4435 with the peak of the hard emission
coincident with the galaxy's optical center; while the peak of the soft X-ray
emission is displaced 316 pc to the NE. The spectrum of NGC 4435 is well fitted
by a non-thermal power law plus a thermal component from 0.2-0.3 keV diffuse
ISM gas. We argue that the X-ray properties of gas outside the nuclear region
in NGC4438 and in NGC4435 favor a high velocity, off-center collision between
these galaxies ~ 100 Myr ago; while the nuclear X-ray emitting outflow gas in
NGC4438 has been heated only recently (within ~ 1-2 Myr) by shocks (v_s ~ 600
kms^{-1}) possibly powered by a central AGN.Comment: 40 pages, 7 figures; minor changes to conform to published version,
improved spectral fits to NGC 4435, improved figures 3,5; new figures 6b,
Buoyant AGN bubbles in the quasi-isothermal potential of NGC 1399
The Fornax Cluster is a low-mass cool-core galaxy cluster. We present a deep
{\sl Chandra} study of NGC 1399, the central dominant elliptical galaxy of
Fornax. The cluster center harbors two symmetric X-ray cavities coincident with
a pair of radio lobes fed by two collimated jets along a north-south axis. A
temperature map reveals that the AGN outburst has created a channel filled with
cooler gas out to a radius of 10 kpc. The cavities are surrounded by cool
bright rims and filaments that may have been lifted from smaller radii by the
buoyant bubbles. X-ray imaging suggests a potential ghost bubble of
5\,kpc diameter to the northwest. We find that the amount of gas lifted by AGN
bubbles is comparable to that which would otherwise cool, demonstrating that
AGN driven outflow is effective in offsetting cooling in low-mass clusters. The
cluster cooling time scale is times longer than the dynamical time scale,
which is consistent with the lack of cold molecular gas at the cluster center.
The X-ray hydrostatic mass is consistent within 10\% with the total mass
derived from the optical data. The observed entropy profile rises linearly,
following a steeper slope than that observed at the centers of massive
clusters; gas shed by stars in NGC 1399 may be incorporated in the hot phase.
However, it is far-fetched for supernova-driven outflow to produce and maintain
the thermal distribution in NGC 1399 and it is in tension with the metal
content in the hot gas.Comment: 11 pages, 6 figures, Matches the version published in Ap
Capturing the 3D motion of an infalling galaxy via fluid dynamics
The Fornax Cluster is the nearest galaxy cluster in the southern sky. NGC 1404 is a bright elliptical galaxy falling through the intracluster medium of the Fornax Cluster. The sharp leading edge of NGC 1404 forms a classical "cold front" that separates 0.6 keV dense interstellar medium and 1.5 keV diffuse intracluster medium. We measure the angular pressure variation along the cold front using a very deep (670\,ksec) {\sl Chandra} X-ray observation. We are taking the classical approach -- using stagnation pressure to determine a substructure's speed -- to the next level by not only deriving a general speed but also directionality which yields the complete velocity field as well as the distance of the substructure directly from the pressure distribution. We find a hydrodynamic model consistent with the pressure jump along NGC 1404's atmosphere measured in multiple directions. The best-fit model gives an inclination of 33∘ and a Mach number of 1.3 for the infall of NGC 1404, in agreement with complementary measurements of the motion of NGC 1404. Our study demonstrates the successful treatment of a highly ionized ICM as ideal fluid flow, in support of the hypothesis that magnetic pressure is not dynamically important over most of the virial region of galaxy clusters
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