98,928 research outputs found
Subaru Weak Lensing Study of Seven Merging Clusters: Distributions of Mass and Baryons
We present and compare projected distributions of mass, galaxies, and the
intracluster medium (ICM) for a sample of merging clusters of galaxies based on
the joint weak-lensing, optical photometric, and X-ray analysis. Our sample
comprises seven nearby Abell clusters, for which we have conducted systematic,
deep imaging observations with Suprime-Cam on Subaru telescope. Our seven
target clusters, representing various merging stages and conditions, allow us
to investigate in details the physical interplay between dark matter, ICM, and
galaxies associated with cluster formation and evolution. A1750 and A1758 are
binary systems consisting of two cluster-sized components, A520, A754, A1758N,
A1758S, and A1914 are on-going cluster mergers, and A2034 and A2142 are
cold-front clusters. In the binary clusters, the projected mass, optical light,
and X-ray distributions are overall similar and regular without significant
substructures. On-going and cold-front merging clusters, on the other hand,
reveal highly irregular mass distributions. Overall the mass distribution
appears to be similar to the galaxy luminosity distribution, whereas their
distributions are quite different from the ICM distribution in a various ways.
We also measured for individual targets the global cluster parameters such as
the cluster mass,the mass-to-light ratio, and the ICM temperature. A comparison
of the ICM and virial temperatures of merging clusters from X-ray and
weak-lensing analyses, respectively, shows that the ICM temperature of on-going
and cold-front clusters is significantly higher than the cluster virial
temperature by a factor of . This temperature excess in the ICM could
be explained by the effects of merger boosts.Comment: "High-resolution pictures available at
http://www.astr.tohoku.ac.jp/~okabe/files/7merger_color.pdf". The published
version is available on-line free of charge by the end of 2008 at
http://pasj.asj.or.jp/v60/n2/600223/600223.pd
J0454-0309: Evidence for a strong lensing fossil group falling into a poor galaxy cluster
We have discovered a strong lensing fossil group (J0454) at z=0.26, projected
near the well-studied cluster MS0451-0305. Using multicolour Subaru/Suprime-Cam
and CFHT/Megaprime imaging together with Keck spectroscopy we identify member
galaxies. A VLT/FORS2 spectrum was taken to determine the redshifts of the
brightest elliptical and the lensed arc. Using HST/ACS images we determine the
group's weak lensing signal and model the strong lens system. This is the first
time that a fossil group is analysed with lensing methods. The X-ray luminosity
and temperature are derived from XMM-Newton data.
We find two filaments extending over 4 Mpc, and within the virial radius we
identify 31 members spectroscopically and 33 via the red sequence with i<22
mag. They segregate into spirals and a dynamically cooler central concentration
of ellipticals with a velocity dispersion of 480 km/s. Weak lensing and cluster
richness relations yield r200 = 830 kpc and M200 = 0.85 x 10^14 Msun. The
brightest group galaxy (BGG) is inconsistent with the dynamic centre of J0454.
It strongly lenses a galaxy at z~2.1, and we model the lens with a
pseudo-isothermal elliptical mass distribution. A large external shear requires
that the BGG must be offset from J0454's dark halo centre by at least 90-130
kpc. The X-ray halo is offset by 24 kpc from the BGG, shows no signs of a
cooling flow and is well described by a beta-model. With L = 1.4 x 10^43 erg/s
J0454 falls well onto standard X-ray cluster scaling relations, but appears
cooler (1.1 keV) than expected (2 keV). We conclude that J0454 consists of two
systems, a sparse cluster and an infalling fossil group, the latter seeding the
BCG. An alternative explanation is that galaxies in a filament, projected along
the line of sight, stream towards the denser fossil group.Comment: 20 pages, 17 figures; Identical to the publication in A+A. Small
language corrections. Minor additions: We check the influence of individual
galaxy haloes to the external shear (Sect. 8.1.1). Alternative interpretation
of the data: Galaxies ina filament projected along the l.o.s. fall into the
fossil group (Section 8.1.2
Machine learning -- based diffractive imaging with subwavelength resolution
Far-field characterization of small objects is severely constrained by the
diffraction limit. Existing tools achieving sub-diffraction resolution often
utilize point-by-point image reconstruction via scanning or labelling. Here, we
present a new imaging technique capable of fast and accurate characterization
of two-dimensional structures with at least wavelength/25 resolution, based on
a single far-field intensity measurement. Experimentally, we realized this
technique resolving the smallest-available to us 180-nm-scale features with
532-nm laser light. A comprehensive analysis of machine learning algorithms was
performed to gain insight into the learning process and to understand the flow
of subwavelength information through the system. Image parameterization,
suitable for diffractive configurations and highly tolerant to random noise was
developed. The proposed technique can be applied to new characterization tools
with high spatial resolution, fast data acquisition, and artificial
intelligence, such as high-speed nanoscale metrology and quality control, and
can be further developed to high-resolution spectroscop
The Magellan/IMACS Catalog of Optical Supernova Remnant Candidates in M83
We present a new optical imaging survey of supernova remnants in M83, using
data obtained with the Magellan I 6.5m telescope and IMACS instrument under
conditions of excellent seeing. Using the criterion of strong [S II] emission
relative to Halpha, we confirm all but three of the 71 SNR candidates listed in
our previous survey, and expand the SNR candidate list to 225 objects, more
than tripling the earlier sample. Comparing the optical survey with a new deep
X-ray survey of M83 with Chandra, we find 61 of these SNR candidates to have
X-ray counterparts. We also identify an additional list of 46 [O III] -selected
nebulae for follow-up as potential ejecta-dominated remnants, seven of which
have associated X-ray emission that makes them strong candidates. Some of the
other [O III]-bright objects could also be normal ISM-dominated supernova
remnants with shocks fast enough to doubly ionize oxygen, but with Halpha and
[S II] emission faint enough to have been missed. A few of these objects may
also be H II regions with abnormally high [O III] emission compared with the
majority of M83 H II regions, compact nebulae excited by young Wolf-Rayet
stars, or even background AGN. The supernova remnant Halpha luminosity function
in M83 is shifted a factor of ~ 4.5x higher than for M33 supernova remnants,
indicative of a higher mean ISM density in M83. We describe the search
technique used to identify the supernova remnant candidates and provide basic
information and finder charts for the objects.Comment: 40 pages, 15 figures, accepted for ApJ
Convolutional Neural Networks Applied to Neutrino Events in a Liquid Argon Time Projection Chamber
We present several studies of convolutional neural networks applied to data
coming from the MicroBooNE detector, a liquid argon time projection chamber
(LArTPC). The algorithms studied include the classification of single particle
images, the localization of single particle and neutrino interactions in an
image, and the detection of a simulated neutrino event overlaid with cosmic ray
backgrounds taken from real detector data. These studies demonstrate the
potential of convolutional neural networks for particle identification or event
detection on simulated neutrino interactions. We also address technical issues
that arise when applying this technique to data from a large LArTPC at or near
ground level
X-ray observations of RX J0822-4300 and Puppis-A
Based on observations with the X-ray observatories Chandra and XMM-Newton we
present results from a detailed spectro-imaging and timing analysis of the
central compact X-ray source RX J0822-4300 in the supernova remnant Puppis-A.
The superior angular resolution of Chandra allows for the first time to
pinpoint the point source nature of this object down to arcsec
(FWHM) and to determine its position:{RA=,
Dec= (J2000)} with sub-arcsecond accuracy.
Spectral fits based on Chandra and XMM-Newton data provide a tight constraint
on the emission properties of RX J0822-4300. Most of its X-ray emission seems
to be of thermal origin. A model spectrum consisting of two blackbody
components with K,
K and km, km for the blackbody temperatures
and the size of the projected emitting regions, respectively, provides the best
model description of its spectrum. A search for X-ray pulsations from RX
J0822-4300, revealed an interesting periodicity candidate which, if confirmed,
does not support a scenario of steady spin-down.Comment: Accepted by A&A, 20 pages, 10 figures, 3 table
p3d: a general data-reduction tool for fiber-fed integral-field spectrographs
The reduction of integral-field spectrograph (IFS) data is demanding work.
Many repetitive operations are required in order to convert raw data into,
typically a large number of, spectra. This effort can be markedly simplified
through the use of a tool or pipeline, which is designed to complete many of
the repetitive operations without human interaction. Here we present our
semi-automatic data-reduction tool p3d that is designed to be used with
fiber-fed IFSs. Important components of p3d include a novel algorithm for
automatic finding and tracing of spectra on the detector, and two methods of
optimal spectrum extraction in addition to standard aperture extraction. p3d
also provides tools to combine several images, perform wavelength calibration
and flat field data. p3d is at the moment configured for four IFSs. In order to
evaluate its performance we have tested the different components of the tool.
For these tests we used both simulated and observational data. We demonstrate
that for three of the IFSs a correction for so-called cross-talk due to
overlapping spectra on the detector is required. Without such a correction
spectra will be inaccurate, in particular if there is a significant intensity
gradient across the object. Our tests showed that p3d is able to produce
accurate results. p3d is a highly general and freely available tool. It is
easily extended to include improved algorithms, new visualization tools and
support for additional instruments. The program code can be downloaded from the
p3d-project web site http://p3d.sourceforge.netComment: 18 pages, 15 figures, 3 tables, accepted for publication in A&
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