635 research outputs found
Shape, shear & flexion: An analytic flexion formalism for realistic mass profiles
Flexion is a non-linear gravitational lensing effect that arises from
gradients in the convergence and shear across an image. We derive a formalism
that describes non-linear gravitational lensing by a circularly symmetric lens
in the thin-lens approximation. This provides us with relatively simple
expressions for first- and second-flexion in terms of only the surface density
and projected mass distribution of the lens. We give details of exact lens
models, in particular providing flexion calculations for a Sersic-law profile,
which has become increasingly popular over recent years. We further provide a
single resource for the analytic forms of convergence, shear, first- and
second-flexion for the following mass distributions: a point mass, singular
isothermal sphere (SIS); Navarro-Frenk-White (NFW) profile; Sersic-law profile.
We quantitatively compare these mass distributions and show that the
convergence and first-flexion are better indicators of the Sersic shape
parameter, while for the concentration of NFW profiles the shear and
second-flexion terms are preferred.Comment: Accepted for publication in MNRA
Identificação de mecanismos envolvidos na resposta de bovinos ao carrapato Rhipicephalus microplus.
O objetivo desse trabalho foi identificar grupos de genes envolvidos na resposta de bovinos à infestação artificial com o carrapato Rhipicephalus microplus, por meio da construção de redes gênicas. Dados de um experimento com microarranjos, provenientes da hibridização de amostras de pele de fêmeas cruzadas Senepol x Nelore, Angus x Nelore e Nelore, obtidas antes (A) e (D) após a infestação artificial com o carrapato, foram analisados por meio de uma metodologia de construção de redes baseada em co-expressão gênica (WGCNA). Os dados foram pré-processados usando os pacotes affy e gcrma do R/Bioconductor e as redes de co-expressão identificadas separadamente para cada grupo (A e D), pelo pacote R/WGCNA. As redes foram comparadas e os módulos não conservados entre os dois grupos foram identificados a partir de um teste de correlação dos valores de conectividade. Nossa análise identificou 8 módulos de genes co-expressos, sendo um deles (6) não conservado entre os grupos. O modulo 6 (n=85 genes) mostrou-se enrique ido para o processo biológico Proteólise, sugerindo o envolvimento desse processo e dos genes identificados (ADAMTS4, CASP4, C3, CFB, PRSS22 e SPCS3) na resposta dos animais à infestação
Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps
Supermassive black hole binary systems (SMBHB) are standard sirens -- the
gravitational wave analogue of standard candles -- and if discovered by
gravitational wave detectors, they could be used as precise distance
indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB
signals, seriously degrading any distance measurements. Using a weak lensing
map of the SMBHB line of sight, we can estimate its magnification and thereby
remove some uncertainty in its distance, a procedure we call "delensing." We
find that delensing is significantly improved when galaxy shears are combined
with flexion measurements, which reduce small-scale noise in reconstructed
magnification maps. Under a Gaussian approximation, we estimate that delensing
with a 2D mosaic image from an Extremely Large Telescope (ELT) could reduce
distance errors by about 30-40% for a SMBHB at z=2. Including an additional
wide shear map from a space survey telescope could reduce distance errors by
50%. Such improvement would make SMBHBs considerably more valuable as
cosmological distance probes or as a fully independent check on existing
probes.Comment: 9 pages, 4 figures, submitted to MNRA
Removing epoxy underfill between neighbouring components using acid for component chip-off
International audienc
The Hyper Suprime-Cam Software Pipeline
In this paper, we describe the optical imaging data processing pipeline
developed for the Subaru Telescope's Hyper Suprime-Cam (HSC) instrument. The
HSC Pipeline builds on the prototype pipeline being developed by the Large
Synoptic Survey Telescope's Data Management system, adding customizations for
HSC, large-scale processing capabilities, and novel algorithms that have since
been reincorporated into the LSST codebase. While designed primarily to reduce
HSC Subaru Strategic Program (SSP) data, it is also the recommended pipeline
for reducing general-observer HSC data. The HSC pipeline includes high level
processing steps that generate coadded images and science-ready catalogs as
well as low-level detrending and image characterizations.Comment: 39 pages, 21 figures, 2 tables. Submitted to Publications of the
Astronomical Society of Japa
Electron paramagnetic resonance and other properties of hydrogenases isolated from Desulfovibrio vulgaris (strain Hildenborough) and Megasphaera elsdenii
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65872/1/j.1432-1033.1983.tb07727.x.pd
Resolving the discrepancy between lensing and X-ray mass estimates of the complex galaxy cluster Abell 1689
There is a long-standing discrepancy between galaxy cluster masses determined
from X-ray and gravitational lensing observations of which Abell 1689 is a
well-studied example. In this work we take advantage of 180 ks of Chandra X-ray
observations and a new weak gravitational study based on a Hubble Space
Telescope mosaic covering the central 1.8 Mpc x 1.4 Mpc to eliminate the mass
discrepancy. In contrast to earlier X-ray analyses where the very circular
surface brightness has been inferred as Abell 1689 being spherically symmetric
and in hydrostatic equilibrium, a hardness ratio map analysis reveals a regular
and symmetric appearing main clump with a cool core plus some substructure in
the North Eastern part of the cluster. The gravitational lensing mass model
supports the interpretation of Abell 1689 being composed of a main clump, which
is possibly a virialized cluster, plus some substructure. In order to avoid
complications and mis-interpretations due to X-ray emission from the
substructure, we exclude it from the mass reconstruction. Comparing X-ray and
lensing mass profiles of the regular main part only, shows no significant
discrepancy between the two methods and the obtained mass profiles are
consistent over the full range where the mass can be reconstructed from X-rays
(out to approx. 1 Mpc). The obtained cluster mass within approx. 875 kpc
derived from X-rays alone is 6.4 plus/minus 2.1 x 10^14 solar masses compared
to a weak lensing mass of 8.6 plus/minus 3.0 x 10^14 solar masses within the
same radius.Comment: 9 pages, 10 figures, accepted by Ap
Constraining primordial non-Gaussianity with cosmological weak lensing: shear and flexion
We examine the cosmological constraining power of future large-scale weak
lensing surveys on the model of \emph{Euclid}, with particular reference to
primordial non-Gaussianity. Our analysis considers several different estimators
of the projected matter power spectrum, based on both shear and flexion, for
which we review the covariances and Fisher matrices. The bounds provided by
cosmic shear alone for the local bispectrum shape, marginalized over
, are at the level of . We consider
three additional bispectrum shapes, for which the cosmic shear constraints
range from (equilateral shape) up to (orthogonal shape). The competitiveness of cosmic
flexion constraints against cosmic shear ones depends on the galaxy intrinsic
flexion noise, that is still virtually unconstrained. Adopting the very high
value that has been occasionally used in the literature results in the flexion
contribution being basically negligible with respect to the shear one, and for
realistic configurations the former does not improve significantly the
constraining power of the latter. Since the flexion noise decreases with
decreasing scale, by extending the analysis up to
cosmic flexion, while being still subdominant, improves the shear constraints
by when added. However on such small scales the highly non-linear
clustering of matter and the impact of baryonic physics make any error
estimation uncertain. By considering lower, and possibly more realistic, values
of the flexion intrinsic shape noise results in flexion constraining power
being a factor of better than that of shear, and the bounds on
and being improved by a factor of upon
their combination. (abridged)Comment: 30 pages, 4 figures, 4 tables. To appear on JCA
GREAT3 results I: systematic errors in shear estimation and the impact of real galaxy morphology
We present first results from the third GRavitational lEnsing Accuracy
Testing (GREAT3) challenge, the third in a sequence of challenges for testing
methods of inferring weak gravitational lensing shear distortions from
simulated galaxy images. GREAT3 was divided into experiments to test three
specific questions, and included simulated space- and ground-based data with
constant or cosmologically-varying shear fields. The simplest (control)
experiment included parametric galaxies with a realistic distribution of
signal-to-noise, size, and ellipticity, and a complex point spread function
(PSF). The other experiments tested the additional impact of realistic galaxy
morphology, multiple exposure imaging, and the uncertainty about a
spatially-varying PSF; the last two questions will be explored in Paper II. The
24 participating teams competed to estimate lensing shears to within systematic
error tolerances for upcoming Stage-IV dark energy surveys, making 1525
submissions overall. GREAT3 saw considerable variety and innovation in the
types of methods applied. Several teams now meet or exceed the targets in many
of the tests conducted (to within the statistical errors). We conclude that the
presence of realistic galaxy morphology in simulations changes shear
calibration biases by per cent for a wide range of methods. Other
effects such as truncation biases due to finite galaxy postage stamps, and the
impact of galaxy type as measured by the S\'{e}rsic index, are quantified for
the first time. Our results generalize previous studies regarding sensitivities
to galaxy size and signal-to-noise, and to PSF properties such as seeing and
defocus. Almost all methods' results support the simple model in which additive
shear biases depend linearly on PSF ellipticity.Comment: 32 pages + 15 pages of technical appendices; 28 figures; submitted to
MNRAS; latest version has minor updates in presentation of 4 figures, no
changes in content or conclusion
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