356 research outputs found
Discovery of a large-scale filament connected to the massive galaxy cluster MACSJ0717.5+3745 at z=0.55
We report the detection of a 4/h70 Mpc long large-scale filament leading into
the massive galaxy cluster MACS J0717.5+3745. The extent of this object well
beyond the cluster's nominal virial radius (~2.3 Mpc) rules out prior
interaction between its constituent galaxies and the cluster and makes it a
prime candidate for a genuine filament as opposed to a merger remnant or a
double cluster. The structure was discovered as a pronounced overdensity of
galaxies selected to have V-R colors close to the cluster red sequence.
Extensive spectroscopic follow-up of over 300 of these galaxies in a region
covering the filament and the cluster confirms that the entire structure is
located at the cluster redshift of z=0.545. Featuring galaxy surface densities
of typically 15/Mpc^2 down to luminosities of 0.10 L(*,V), the most diffuse
parts of the filament are comparable in density to the clumps of red galaxies
found around A851 in the only similar study carried out to date (Kodama et
al.). Our direct detection of an extended large-scale filament funneling matter
onto a massive, distant cluster provides a superb target for in-depth studies
of the evolution of galaxies in environments of greatly varying density, and
supports the predictions from theoretical models and numerical simulations of
structure formation in a hierarchical picture.Comment: ApJL, in pres
Large-Scale Sunyaev-Zel'dovich Effect: Measuring Statistical Properties with Multifrequency Maps
We study the prospects for extracting detailed statistical properties of the
Sunyaev-Zel'dovich (SZ) effect associated with large scale structure using
upcoming multifrequency CMB experiments. The greatest obstacle to detecting the
large-angle signal is the confusion noise provided by the primary anisotropies
themselves, and to a lesser degree galactic and extragalactic foregrounds. We
employ multifrequency subtraction techniques and the latest foregrounds models
to determine the detection threshold for the Boomerang, MAP (several microK)
and Planck CMB (sub microK) experiments. Calibrating a simplified biased-tracer
model of the gas pressure off recent hydrodynamic simulations, we estimate the
SZ power spectrum, skewness and bispectrum through analytic scalings and N-body
simulations of the dark matter. We show that the Planck satellite should be
able to measure the SZ effect with sufficient precision to determine its power
spectrum and higher order correlations, e.g. the skewness and bispectrum.
Planck should also be able to detect the cross correlation between the SZ and
gravitational lensing effect in the CMB. Detection of these effects will help
determine the properties of the as yet undetected gas, including the manner in
which the gas pressure traces the dark matter.Comment: 13 ApJ pages, 11 figures; typos and figure 5 revised; submitted to
Ap
XMM-Newton study of A3562 and its immediate Shapley environs
Using the mosaic of six XMM-Newton observations, we study the hydrodynamic
state of the A3562, a cluster in the center of the Shapley Supercluster. The
X-ray image reveals a sharp surface brightness gradient within the core of
A3562, a 200 kpc ridge extending to the south-west. A nearby group, SC1329-313,
imaged within this program also exhibits a tail aligned with the ridge. Study
of the pressure and entropy identified the ridge with a 40% pressure
enhancement. An associated Mach number of 1.15 relative to a polytropic sound
speed for a 5 keV plasma requires the velocity of the group to be 1400 km/s,
while the projected velocity difference between the cluster and the group
amounts to 1200-1500 km/s. Apparent disruption of the group, if attributed to
the ram pressure, also requires the velocity of the group in the cluster frame
to amount to 1700+/-150 km/s. The sharp surface brightness gradient at the
center is identified with a contact discontinuity, which together with dove
tails in the the large-scale entropy distribution reveals a sloshing of the BCG
in response to the passage of the SC1329-313 group. Using the extent of the
low-entropy tails in A3562 we estimate the amplitude of sloshing motion to be
200/h_70 kpc and the oscillation frequency 1 Gyr.Comment: ApJ in press, 10 page
Disaster financing and poverty traps for poor households: Realities in Northern India
This paper addresses household-level disaster financing strategies of the poor in developing countries within the context of current poverty trap discussions. It presents findings on risk perceptions and loss financing practices in relation to floods and droughts in Uttar Pradesh, India. The study found that, due to financial shocks, the risk of households falling below the subsistence level and into a poverty trap is high. In this context, the paper links current approaches in household welfare-drive disaster risk financing to the survey results and provides policy recommendations
Laser-Cluster-Interaction in a Nanoplasma-Model with Inclusion of Lowered Ionization Energies
The interaction of intense laser fields with silver and argon clusters is
investigated theoretically using a modified nanoplasma model. Single pulse and
double pulse excitations are considered. The influence of the dense cluster
environment on the inner ionization processes is studied including the lowering
of the ionization energies. There are considerable changes in the dynamics of
the laser-cluster interaction. Especially, for silver clusters, the lowering of
the ionization energies leads to increased yields of highly charged ions.Comment: 10 pages, 11 figure
XMM-Newton discovery of an X-ray filament in Coma
XMM-Newton observations of the outskirts of the Coma cluster of galaxies
confirm the existence of a soft X-ray excess claimed previously and show it
comes from warm thermal emission. Our data provide a robust estimate of its
temperature (~0.2 keV) and oxygen abundance (~0.1 solar). Using a combination
of XMM-Newton and ROSAT All-Sky Survey data, we rule out a Galactic origin of
the soft X-ray emission. Associating this emission with a 20 Mpc region in
front of Coma, seen in the skewness of its galaxy velocity distribution, yields
an estimate of the density of the warm gas of ~50 f_baryon rho_critical, where
f_baryon is the baryon fraction of the gas and rho_critical is the critical
density needed to halt the expansion of the universe. Our measurement of the
gas mass associated with the warm emission strongly support its nonvirialized
nature, suggesting that we are observing the warm-hot intergalactic medium
(WHIM). Our measurements provide a direct estimate of the O, Ne and Fe
abundance of the WHIM. Differences with the reported Ne/O ratio for some OVI
absorbers hints at a different origin of the OVI absorbers and the Coma
filament. We argue that the Coma filament has likely been preheated, but at a
substantially lower level compared to what is seen in the outskirts of groups.
The thermodynamic state of the gas in the Coma filament reduces the
star-formation rate in the embedded spiral galaxies, providing an explanation
for the presence of passive spirals observed in this and other clusters.Comment: 9 pages, 5 figures, accepted by A&
Glacier mass balance reconstruction by sublimation induced enrichment of chemical species on Cerro Tapado (Chilean Andes)
A 36 m long ice core down to bedrock from the Cerro Tapado glacier (5536 m a.s.l, 30°08' S, 69°55' W) was analyzed to reconstruct past climatic conditions for Northern Chile. Because of the marked seasonality in the precipitation (short wet winter and extended dry summer periods) in this region, major snow ablation and related post-depositional processes occur on the glacier surface during summer periods. They include predominantly sublimation and dry deposition. Assuming that, like measured during the field campaign, the enrichment of chloride was always related to sublimation, the chemical record along the ice core may be applied to reconstruct the history of such secondary processes linked to the past climatic conditions over northern Chile. For the time period 1962–1999, a mean annual net accumulation of 316 mm water equivalent (weq) and 327 mm weq loss by sublimation was deduced by this method. This corresponds to an initial total annual accumulation of 539 mm weq. The annual variability of the accumulation and sublimation is related with the Southern Oscillation Index (SOI): higher net-accumulation during El-Niño years and more sublimation during La Niña years. The deepest part of the ice record shows a time discontinuity; with an ice body deposited under different climatic conditions: 290 mm higher precipitation but with reduced seasonal distribution (+470 mm in winter and –180 mm in summer) and –3°C lower mean annual temperature. Unfortunately, its age is unknown. The comparison with regional proxy data however let us conclude that the glacier buildup did most likely occur after the dry mid-Holocene
Is There Still Room for Warm/Hot Gas? Simulating the X-ray Background Spectrum
At low redshifts, a census of the baryons in all known reservoirs falls a
factor of two to four below the total baryon density predicted from Big Bang
nucleosynthesis arguments and observed light element ratios. Recent
cosmological hydrodynamic simulations suggest that a significant fraction of
these missing baryons could be in the form of warm/hot gas in the filaments and
halos within which most field galaxies are embedded. With the release of source
count results from Chandra and recent detections of this gas in O VI quasar
absorption lines, it becomes interesting to examine the predictions and limits
placed on this component of the X-ray background (XRB). We have used new
hydrodynamical simulations to predict the total X-ray spectrum from the gas in
the 100 eV to 10 keV range. We find that, when uncertainties in the
normalization of the observed XRB and the value of Omega_b are taken into
account, our results are consistent with current observational limits placed on
the contribution of emission from gas to the XRB. In the 0.5-2 keV range, we
expect the contribution from this component to be 0.63 10^{-12} erg s^-1 cm^-2
deg^-2 or between 6% and 18% of the extragalactic surface brightness. The peak
fraction occurs in the 0.5-1 keV range where the predicted line emission
mirrors a spectral bump seen in the latest ASCA/ROSAT XRB data.Comment: 5 pages with 1 figure; submitted to ApJ Letter
Leaf venation, as a resistor, to optimize a switchable IR absorber
Leaf vascular patterns are the mechanisms and mechanical support for the transportation of fluidics for photosynthesis and leaf development properties. Vascular hierarchical networks in leaves have far-reaching functions in optimal transport efficiency of functional fluidics. Embedding leaf morphogenesis as a resistor network is significant in the optimization of a translucent thermally functional material. This will enable regulation through pressure equalization by diminishing flow pressure variation. This paper investigates nature’s vasculature networks that exhibit hierarchical branching scaling applied to microfluidics. To enable optimum potential for pressure drop regulation by algorithm design. This code analysis of circuit conduit optimization for transport fluidic flow resistance is validated against CFD simulation, within a closed loop network. The paper will propose this self-optimization, characterization by resistance seeking targeting to determine a microfluidic network as a resistor. To advance a thermally function material as a switchable IR absorber
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