527 research outputs found
An XMM-Newton study of the sub-structure in M87's halo
The high signal to noise and good point spread function of XMM have allowed
the first detailed study of the interaction between the thermal and radio
emitting plasma in the central regions of M87. We show that the X-ray emitting
structure, previously seen by ROSAT, is thermal in nature and that the east and
southwest extensions in M87's X-ray halo have a significantly lower temperature
(kT= 1.5 keV) than the surrounding ambient medium (kT= 2.3 keV). There is
little or no evidence for non-thermal emission with an upper limit on the
contribution of a power law component of spectral index flatter than 3 being
less than 1% of the flux in the region of the radio lobes.Comment: 6 pages, 8 color figures, to be published in A&A, number 36
Substructure of the galaxy clusters in the REXCESS sample: observed statistics and comparison to numerical simulations
We study the substructure statistics of a representative sample of galaxy
clusters by means of two currently popular substructure characterisation
methods, power ratios and centroid shifts. We use the 31 clusters from the
REXCESS sample, compiled from the southern ROSAT All-Sky cluster survey REFLEX
with a morphologically unbiased selection in X-ray luminosity and redshift, all
of which have been reobserved with XMM-Newton. We investigate the uncertainties
of the substructure parameters and examine the dependence of the results on
projection effects, finding that the uncertainties of the parameters can be
quite substantial. Thus while the quantification of the dynamical state of
individual clusters with these parameters should be treated with extreme
caution, these substructure measures provide powerful statistical tools to
characterise trends of properties in large cluster samples. The centre shift
parameter, w, is found to be more sensitive in general. For the REXCESS sample
neither the occurence of substructure nor the presence of cool cores depends on
cluster mass. There is a significant anti-correlation between the existence of
substantial substructure and cool cores. The simulated clusters show on average
larger substructure parameters than the observed clusters, a trend that is
traced to the fact that cool regions are more pronounced in the simulated
clusters, leading to stronger substructure measures in merging clusters and
clusters with offset cores. Moreover, the frequency of cool regions is higher
in the simulations than in the observations, implying that the description of
the physical processes shaping cluster formation in the simulations requires
further improvement.Comment: Mauscript submitted to Astronomy and Astrophysics, 20 figure
Redshift evolution of the 1.4 GHz volume averaged radio luminosity function in clusters of galaxies
By cross-correlating large samples of galaxy clusters with publicly available
radio source catalogs, we construct the volume-averaged radio luminosity
function (RLF) in clusters of galaxies, and investigate its dependence on
cluster redshift and mass. In addition, we determine the correlation between
the cluster mass and the radio luminosity of the brightest source within 50 kpc
from the cluster center. We use two cluster samples: the optically selected
maxBCG cluster catalog and a composite sample of X-ray selected clusters. The
radio data come from the VLA NVSS and FIRST surveys. We use scaling relations
to estimate cluster masses and radii to get robust estimates of cluster
volumes. We determine the projected radial distribution of sources, for which
we find no dependence on luminosity or cluster mass. Background and foreground
sources are statistically accounted for, and we account for confusion of radio
sources by adaptively degrading the resolution of the radio source surveys. We
determine the redshift evolution of the RLF under the assumption that its
overall shape does not change with redshift. Our results are consistent with a
pure luminosity evolution of the RLF in the range 0.1 < z < 0.3 from the
optical cluster sample. The X-ray sample extends to higher redshift and yields
results also consistent with a pure luminosity evolution. We find no direct
evidence of a dependence of the RLF on cluster mass from the present data,
although the data are consistent with the most luminous sources only being
found in high-mass systems.Comment: Accepted for publication in A&
The Representative XMM-Newton Cluster Structure Survey (REXCESS) of an X-ray Luminosity Selected Galaxy Cluster Sample
The largest uncertainty for cosmological studies using clusters of galaxies
is introduced by our limited knowledge of the statistics of galaxy cluster
structure, and of the scaling relations between observables and cluster mass.
To improve on this situation we have started an XMM-Newton Large Programme for
the in-depth study of a representative sample of 33 galaxy clusters, selected
in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having
X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV
band. This paper introduces the sample, compiles properties of the clusters,
and provides detailed information on the sample selection function. We describe
the selection of a nearby galaxy cluster sample that makes optimal use of the
XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity
coverage for the full range from poor clusters to the most massive objects in
the Universe. For the clusters in the sample, X-ray fluxes are derived and
compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We
find that the fluxes and the flux errors have been reliably determined in the
ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample
selection function documented in detail in this paper to determine the X-ray
luminosity function, and compare it with the luminosity function of the entire
REFLEX sample. We also discuss morphological peculiarities of some of the
sample members. The sample and some of the background data given in this
introductory paper will be important for the application of these data in the
detailed studies of cluster structure, to appear in forthcoming publications.Comment: 17 pages, 17 figures; to appear in A&A. A pdf version with
full-quality figures can be found at
ftp://ftp.xray.mpe.mpg.de/people/gwp/xmmlp/xmmlp.pd
eROSITA Science Book: Mapping the Structure of the Energetic Universe
eROSITA is the primary instrument on the Russian SRG mission. In the first
four years of scientific operation after its launch, foreseen for 2014, it will
perform a deep survey of the entire X-ray sky. In the soft X-ray band (0.5-2
keV), this will be about 20 times more sensitive than the ROSAT all sky survey,
while in the hard band (2-10 keV) it will provide the first ever true imaging
survey of the sky at those energies. Such a sensitive all-sky survey will
revolutionize our view of the high-energy sky, and calls for major efforts in
synergic, multi-wavelength wide area surveys in order to fully exploit the
scientific potential of the X-ray data. The design-driving science of eROSITA
is the detection of very large samples (~10^5 objects) of galaxy clusters out
to redshifts z>1, in order to study the large scale structure in the Universe,
test and characterize cosmological models including Dark Energy. eROSITA is
also expected to yield a sample of around 3 millions Active Galactic Nuclei,
including both obscured and un-obscured objects, providing a unique view of the
evolution of supermassive black holes within the emerging cosmic structure. The
survey will also provide new insights into a wide range of astrophysical
phenomena, including accreting binaries, active stars and diffuse emission
within the Galaxy, as well as solar system bodies that emit X-rays via the
charge exchange process. Finally, such a deep imaging survey at high spectral
resolution, with its scanning strategy sensitive to a range of variability
timescales from tens of seconds to years, will undoubtedly open up a vast
discovery space for the study of rare, unpredicted, or unpredictable
high-energy astrophysical phenomena. In this living document we present a
comprehensive description of the main scientific goals of the mission, with
strong emphasis on the early survey phases.Comment: 84 Pages, 52 Figures. Published online as MPE document. Edited by S.
Allen. G. Hasinger and K. Nandra. Few minor corrections (typos) and updated
reference
Self-Assembly from Milli- to Nanoscales: Methods and Applications
The design and fabrication techniques for microelectromechanical systems (MEMS) and nanodevices are progressing rapidly. However, due to material and process flow incompatibilities in the fabrication of sensors, actuators and electronic circuitry, a final packaging step is often necessary to integrate all components of a heterogeneous microsystem on a common substrate. Robotic pick-and-place, although accurate and reliable at larger scales, is a serial process that downscales unfavorably due to stiction problems, fragility and sheer number of components. Self-assembly, on the other hand, is parallel and can be used for device sizes ranging from millimeters to nanometers. In this review, the state-of-the-art in methods and applications for self-assembly is reviewed. Methods for assembling three-dimensional (3D) MEMS structures out of two-dimensional (2D) ones are described. The use of capillary forces for folding 2D plates into 3D structures, as well as assembling parts onto a common substrate or aggregating parts to each other into 2D or 3D structures, is discussed. Shape matching and guided assembly by magnetic forces and electric fields are also reviewed. Finally, colloidal self-assembly and DNA-based self-assembly, mainly used at the nanoscale, are surveyed, and aspects of theoretical modeling of stochastic assembly processes are discussed
A Cilia-inspired Closed-loop Sensor-actuator Array
© 2018, Jilin University. Cilia are finger-like cell-surface organelles that are used by certain varieties of aquatic unicellular organisms for motility, sensing and object manipulation. Initiated by internal generators and external mechanical and chemical stimuli, coordinated undulations of cilia lead to the motion of a fluid surrounding the organism. This motion transports micro-particles towards an oral cavity and provides motile force. Inspired by the emergent properties of cilia possessed by the pond organism P. caudatum, we propose a novel smart surface with closed-loop control using sensor-actuators pairings that can manipulate objects. Each vibrating motor actuator is controlled by a localised microcontroller which utilises proximity sensor information to initiate actuation. The circuit boards are designed to be plug-and-play and are infinitely up-scalable and reconfigurable. The smart surface is capable of moving objects at a speed of 7.2 millimetres per second in forward or reverse direction. Further development of this platform will include more anatomically similar biomimetic cilia and control
Planck Intermediate Results. IV. The XMM-Newton validation programme for new Planck galaxy clusters
We present the final results from the XMM-Newton validation follow-up of new
Planck galaxy cluster candidates. We observed 15 new candidates, detected with
signal-to-noise ratios between 4.0 and 6.1 in the 15.5-month nominal Planck
survey. The candidates were selected using ancillary data flags derived from
the ROSAT All Sky Survey (RASS) and Digitized Sky Survey all-sky maps, with the
aim of pushing into the low SZ flux, high-z regime and testing RASS flags as
indicators of candidate reliability. 14 new clusters were detected by XMM,
including 2 double systems. Redshifts lie in the range 0.2 to 0.9, with 6
clusters at z>0.5. Estimated M500 range from 2.5 10^14 to 8 10^14 Msun. We
discuss our results in the context of the full XMM validation programme, in
which 51 new clusters have been detected. This includes 4 double and 2 triple
systems, some of which are chance projections on the sky of clusters at
different z. We find that association with a RASS-BSC source is a robust
indicator of the reliability of a candidate, whereas association with a FSC
source does not guarantee that the SZ candidate is a bona fide cluster.
Nevertheless, most Planck clusters appear in RASS maps, with a significance
greater than 2 sigma being a good indication that the candidate is a real
cluster. The full sample gives a Planck sensitivity threshold of Y500 ~ 4 10^-4
arcmin^2, with indication for Malmquist bias in the YX-Y500 relation below this
level. The corresponding mass threshold depends on z. Systems with M500 > 5
10^14 Msun at z > 0.5 are easily detectable with Planck. The newly-detected
clusters follow the YX-Y500 relation derived from X-ray selected samples.
Compared to X-ray selected clusters, the new SZ clusters have a lower X-ray
luminosity on average for their mass. There is no indication of departure from
standard self-similar evolution in the X-ray versus SZ scaling properties.
(abridged)Comment: accepted by A&
Magnetic Field Amplification in Galaxy Clusters and its Simulation
We review the present theoretical and numerical understanding of magnetic
field amplification in cosmic large-scale structure, on length scales of galaxy
clusters and beyond. Structure formation drives compression and turbulence,
which amplify tiny magnetic seed fields to the microGauss values that are
observed in the intracluster medium. This process is intimately connected to
the properties of turbulence and the microphysics of the intra-cluster medium.
Additional roles are played by merger induced shocks that sweep through the
intra-cluster medium and motions induced by sloshing cool cores. The accurate
simulation of magnetic field amplification in clusters still poses a serious
challenge for simulations of cosmological structure formation. We review the
current literature on cosmological simulations that include magnetic fields and
outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
- …