46 research outputs found
Weak Lensing Mass Reconstruction of the Galaxy Cluster Abell 209
Weak lensing applied to deep optical images of clusters of galaxies provides
a powerful tool to reconstruct the distribution of the gravitating mass
associated to these structures. We use the shear signal extracted by an
analysis of deep exposures of a region centered around the galaxy cluster Abell
209, at redshift z=0.2, to derive both a map of the projected mass distribution
and an estimate of the total mass within a characteristic radius. We use a
series of deep archival R-band images from CFHT-12k, covering an area of 0.3
deg^2. We determine the shear of background galaxy images using a new
implementation of the modified Kaiser-Squires-Broadhurst pipeline for shear
determination, which we has been tested against the ``Shear TEsting Program 1
and 2'' simulations. We use mass aperture statistics to produce maps of the 2
dimensional density distribution, and parametric fits using both
Navarro-Frenk-White (NFW) and singular-isothermal-sphere profiles to constrain
the total mass. The projected mass distribution shows a pronounced asymmetry,
with an elongated structure extending from the SE to the NW. This is in general
agreement with the optical distribution previously found by other authors. A
similar elongation was previously detected in the X-ray emission map, and in
the distribution of galaxy colours. The circular NFW mass profile fit gives a
total mass of M_{200} = 7.7^{+4.3}_{-2.7} 10^{14} solar masses inside the
virial radius r_{200} = 1.8\pm 0.3 Mpc. The weak lensing profile reinforces the
evidence for an elongated structure of Abell 209, as previously suggested by
studies of the galaxy distribution and velocities.Comment: accepted by A&A, 15 pages, 11 figure
A New Window of Exploration in the Mass Spectrum: Strong Lensing by Galaxy Groups in the SL2S
The existence of strong lensing systems with Einstein radii (Re) covering the
full mass spectrum, from ~1-2" (produced by galaxy scale dark matter haloes) to
>10" (produced by galaxy cluster scale haloes) have long been predicted. Many
lenses with Re around 1-2" and above 10" have been reported but very few in
between. In this article, we present a sample of 13 strong lensing systems with
Re in the range 3"- 8", i.e. systems produced by galaxy group scale dark matter
haloes, spanning a redshift range from 0.3 to 0.8. This opens a new window of
exploration in the mass spectrum, around 10^{13}- 10^{14} M_{sun}, which is a
crucial range for understanding the transition between galaxies and galaxy
clusters. Our analysis is based on multi-colour CFHTLS images complemented with
HST imaging and ground based spectroscopy. Large scale properties are derived
from both the light distribution of the elliptical galaxies group members and
weak lensing of the faint background galaxy population. On small scales, the
strong lensing analysis yields Einstein radii between 2.5" and 8". On larger
scales, the strong lenses coincide with the peak of the light distribution,
suggesting that mass is traced by light. Most of the luminosity maps have
complicated shapes, indicating that these intermediate mass structures are
dynamically young. Fitting the reduced shear with a Singular Isothermal Sphere,
we find sigma ~ 500 km/s and an upper limit of ~900 km/s for the whole sample.
The mass to light ratio for the sample is found to be M/L_i ~ 250 (solar units,
corrected for evolution), with an upper limit of 500. This can be compared to
mass to light ratios of small groups (with sigma ~ 300 km/s and galaxy clusters
with sigma > 1000 km/s, thus bridging the gap between these mass scales.Comment: A&A Accepted. Draft with Appendix images can be found at
http://www.dark-cosmology.dk/~marceau/groups_sl2s.pd
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Optical and tribological properties of diamond-like carbon films synthesized by plasma immersion ion processing
Hard diamond-like carbon (DLC) films have been prepared on PMMA (Polymethyl methacrylate), glass, and Si(100) substrates using C{sub 2}H{sub 2}-Ar plasma immersion ion processing (PIIP). The composition, structure, and properties of the films were investigated with regard to variation of the deposition parameters. It was found that the modulation of reactive gas composition during PIIP could enhance the formation of DLC films with an increased sp{sup 3} bonding structure, improved surface smoothness, high density and high hardness. An optimal combination of good optical properties and high hardness was highly dependent on the control of hydrogen content in the DLC films. Tribological tests showed that DLC-coated glass and PMMA samples exhibited a reduced friction coefficient and enhanced wear resistance relative to uncoated glass and PMMA materials. The effects of ion energy and gas composition during PIIP deposition on the formation of optically transparent and wear resistant DLC films are discussed
Global Properties of the Rich Cluster ABCG 209 at z~0.2. Spectroscopic and Photometric Catalogue
This paper is aimed at giving an overview of the global properties of the
rich cluster of galaxies ABCG 209. This is achieved by complementing the
already available data with new medium resolution spectroscopy and NIR
photometry which allow us to i) analyse in detail the cluster dynamics,
distinguishing among galaxies belonging to different substructures and deriving
their individual velocity distributions, using a total sample of 148 galaxies
in the cluster region, of which 134 belonging to the cluster; ii) derive the
cluster NIR luminosity function; iii) study the Kormendy relation and the
photometric plane of cluster early-type galaxies (ETGs). Finally we provide an
extensive photometric (optical and NIR) and spectroscopic dataset for such a
complex system to be used in further analyses investigating the nature,
formation and evolution of rich clusters of galaxies. The observational
scenario confirms that ABCG 209 is presently undergoing strong dynamical
evolution with the merging of two or more subclumps. This interpretation is
also supported by the detection of a radio halo (Giovannini et al. 2006)
suggesting that there is a recent or ongoing merging. Cluster ETGs follow a
Kormendy relation whose slope is consistent with previous studies both at
optical and NIR wavelengths. We investigate the origin of the intrinsic scatter
of the photometric plane due to trends of stellar populations, using line
indices as indicators of age, metallicity and alpha/Fe enhancement. We find
that the chemical evolution of galaxies could be responsible for the intrinsic
dispersion of the Photometric Plane.Comment: 39 pages, 17 figures, MNRAS in pres
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
HCN emission from translucent gas and UV-illuminated cloud edges revealed by wide-field IRAM 30m maps of Orion B GMC: Revisiting its role as tracer of the dense gas reservoir for star formation
We present 5 deg^2 (~250 pc^2) HCN, HNC, HCO+, and CO J=1-0 maps of the Orion
B GMC, complemented with existing wide-field [CI] 492 GHz maps, as well as new
pointed observations of rotationally excited HCN, HNC, H13CN, and HN13C lines.
We detect anomalous HCN J=1-0 hyperfine structure line emission almost
everywhere in the cloud. About 70% of the total HCN J=1-0 luminosity arises
from gas at A_V < 8 mag. The HCN/CO J=1-0 line intensity ratio shows a bimodal
behavior with an inflection point at A_V < 3 mag typical of translucent gas and
UV-illuminated cloud edges. We find that most of the HCN J=1-0 emission arises
from extended gas with n(H2) < 10^4 cm^-3, even lower density gas if the
ionization fraction is > 10^-5 and electron excitation dominates. This result
explains the low-A_V branch of the HCN/CO J=1-0 intensity ratio distribution.
Indeed, the highest HCN/CO ratios (~0.1) at A_V < 3 mag correspond to regions
of high [CI] 492 GHz/CO J=1-0 intensity ratios (>1) characteristic of
low-density PDRs. Enhanced FUV radiation favors the formation and excitation of
HCN on large scales, not only in dense star-forming clumps. The low surface
brightness HCN and HCO+ J=1-0 emission scale with I_FIR (a proxy of the stellar
FUV radiation field) in a similar way. Together with CO J=1-0, these lines
respond to increasing I_FIR up to G0~20. On the other hand, the bright HCN
J=1-0 emission from dense gas in star-forming clumps weakly responds to I_FIR
once the FUV radiation field becomes too intense (G0>1500). The different power
law scalings (produced by different chemistries, densities, and line excitation
regimes) in a single but spatially resolved GMC resemble the variety of
Kennicutt-Schmidt law indexes found in galaxy averages. As a corollary for
extragalactic studies, we conclude that high HCN/CO J=1-0 line intensity ratios
do not always imply the presence of dense gas.Comment: accepted for publication in A&A. 24 pages, 18 figures, plus Appendix.
Abridged Abstract. English language not edite
Deep learning denoising by dimension reduction: Application to the ORION-B line cubes
Context. The availability of large bandwidth receivers for millimeter radio
telescopes allows the acquisition of position-position-frequency data cubes
over a wide field of view and a broad frequency coverage. These cubes contain
much information on the physical, chemical, and kinematical properties of the
emitting gas. However, their large size coupled with inhomogenous
signal-to-noise ratio (SNR) are major challenges for consistent analysis and
interpretation.Aims. We search for a denoising method of the low SNR regions of
the studied data cubes that would allow to recover the low SNR emission without
distorting the signals with high SNR.Methods. We perform an in-depth data
analysis of the 13 CO and C 17 O (1 -- 0) data cubes obtained as part of the
ORION-B large program performed at the IRAM 30m telescope. We analyse the
statistical properties of the noise and the evolution of the correlation of the
signal in a given frequency channel with that of the adjacent channels. This
allows us to propose significant improvements of typical autoassociative neural
networks, often used to denoise hyperspectral Earth remote sensing data.
Applying this method to the 13 CO (1 -- 0) cube, we compare the denoised data
with those derived with the multiple Gaussian fitting algorithm ROHSA,
considered as the state of the art procedure for data line cubes.Results. The
nature of astronomical spectral data cubes is distinct from that of the
hyperspectral data usually studied in the Earth remote sensing literature
because the observed intensities become statistically independent beyond a
short channel separation. This lack of redundancy in data has led us to adapt
the method, notably by taking into account the sparsity of the signal along the
spectral axis. The application of the proposed algorithm leads to an increase
of the SNR in voxels with weak signal, while preserving the spectral shape of
the data in high SNR voxels.Conclusions. The proposed algorithm that combines a
detailed analysis of the noise statistics with an innovative autoencoder
architecture is a promising path to denoise radio-astronomy line data cubes. In
the future, exploring whether a better use of the spatial correlations of the
noise may further improve the denoising performances seems a promising avenue.
In addition
Evolution of Gaussian wave packets in capillary jets
A temporal analysis of the evolution of Gaussian wave packets in cylindrical capillary jets is
presented through both a linear two-mode formulation and a one-dimensional nonlinear numerical
scheme. These analyses are normally applicable to arbitrary initial conditions but our study focuses
on pure-impulsive ones. Linear and nonlinear findings give consistent results in the stages for which
the linear theory is valid. The inverse Fourier transforms representing the formal linear solution
for the jet shape is both numerically evaluated and approximated by closed formulas. After a
transient, these formulas predict an almost Gaussian-shape deformation with (i) a progressive drift
of the carrier wave number to that given by the maximum of the Rayleigh dispersion relation, (ii)
a progressive increase of its bell width, and (iii) a quasi-exponential growth of its amplitude. These
parameters agree with those extracted from the fittings of Gaussian wave packets to the numerical
simulations. Experimental results are also reported on near-Gaussian pulses perturbing the exit
velocity of a 2 mm diameter water jet. The possibility of controlling the breakup location along the
jet and other features, such as pinch-off simultaneity, are demonstrated
SINTESIS MAGNETIT (Fe3O4) NANOPARTIKEL DENGAN NATRIUM DODESIL SULFAT
Telah dilakukan sintesis magnetit (Fe3O4) nanopartikel dengan Natrium Dodesil Sulfat (NaDS). Penelitian ini bertujuan untuk mengetahui pengaruh NaDS terhadap karakter kimia dan fisik magnetit nanopartikel hasil sintesis dengan metode kopresipitasi. Sintesis magnetit nanopartikel dilakukan dengan mereaksikan FeSO4.7H2O dan FeCl3.6H2O dengan perbandingan mol 1:2 serta natrium hidroksida (NaOH) sebagai presipitan dengan proses pengadukan pada suhu 60 °C selama 2 jam. Kajian pengaruh surfaktan pada sintesis magnetit nanopartikel dilakukan dengan variasi konsentrasi NaDS dari 1%, 3% dan 6% (b/v). Material hasil sintesis dikarakterisasi dengan spektrofotometer X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), Scanning Electron Microscope-Energy Dispersive X-ray (SEM-EDX) dan Surface Area Analyzer (SAA). Hasil penelitian menunjukkan bahwa magnetit nanopartikel berhasil disintesis. Magnetit ditunjukkan oleh puncak difraksi utama pada 2θ 30,43o; 35,53o; 43,46o; 57,32o dan 62,84o. Ikatan Fe–O ditunjukkan dengan puncak serapan 565 cm-1 yang dianalisa lebih lanjut menggunakan EDX menunjukkan adanya unsur Fe dan O. Adanya surfaktan NaDS menaikkan ukuran partikel dan ukuran kristal magnetit dengan meningkatnya konsentrasi NaDS yang ditambahkan. Morfologi magnetit-NaDS semakin homogen berbentuk butiran-butiran kecil (grain) dengan ukuran partikel sekitar 30-100 nm. Ukuran kristal magnetit sebesar 11,07 nm (magnetit tanpa surfaktan); 13,62 nm (magnetit-NaDS 1%); 16,12 nm (magnetit-NaDS 3%) dan 11,17 nm (magnetit-NaDS 6%). Luas permukaan magnetit nanopartikel berturut-turut sebesar 89,67 m2/g (magnetit tanpa surfaktan); 102,50 m2/g (magnetit-NaDS 1%); 98,45 m2/g (magnetit-NaDS 3%) dan 82,92 m2/g (magnetit-NaDS 6%)
The XXL Survey IV. Mass-temperature relation of the bright cluster sample
The XXL survey is the largest survey carried out by XMM-Newton. Covering an area of 50deg, the survey contains galaxy clusters out to a redshift 2 and to an X-ray flux limit of . This paper is part of the first release of XXL results focussed on the bright cluster sample. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation is used to estimate the mass of all 100 clusters in XXL-100-GC. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS catalog, we derive the of each system with careful considerations of the systematics. The clusters lie at and span a range of . We combine our sample with 58 clusters from the literature, increasing the range out to 10keV. To date, this is the largest sample of clusters with measurements that has been used to study the mass-temperature relation. The fit () to the XXL clusters returns a slope and intrinsic scatter ; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, and . Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further