751 research outputs found
The strongest gravitational lenses: I. The statistical impact of cluster mergers
For more than a decade now, it has been controversial whether or not the high
rate of giant gravitational arcs and the largest observed Einstein radii are
consistent with the standard cosmological model. Recent studies indicate that
mergers provide an efficient mechanism to substantially increase the
strong-lensing efficiency of individual clusters. Based on purely semi-analytic
methods, we investigated the statistical impact of cluster mergers on the
distribution of the largest Einstein radii and the optical depth for giant
gravitational arcs of selected cluster samples. Analysing representative
all-sky realizations of clusters at redshifts z < 1 and assuming a constant
source redshift of z_s = 2.0, we find that mergers increase the number of
Einstein radii above 10 arcsec (20 arcsec) by ~ 35 % (~ 55 %). Exploiting the
tight correlation between Einstein radii and lensing cross sections, we infer
that the optical depth for giant gravitational arcs with a length-to-width
ratio > 7.5 of those clusters with Einstein radii above 10 arcsec (20 arcsec)
increases by ~ 45 % (85 %). Our findings suggest that cluster mergers
significantly influence in particular the statistical lensing properties of the
strongest gravitational lenses. We conclude that semi-analytic studies must
inevitably take these events into account before questioning the standard
cosmological model on the basis of the largest observed Einstein radii and the
statistics of giant gravitational arcs.Comment: 23 pages, 18 figures; accepted for publication in Astronomy and
Astrophysics; v2: minor corrections (added clarifying comments; added Fig.
19) to match the accepted versio
Reconstruction of the two-dimensional gravitational potential of galaxy clusters from X-ray and Sunyaev-Zel'dovich measurements
The mass of galaxy clusters is not a direct observable, nonetheless it is
commonly used to probe cosmological models. Based on the combination of all
main cluster observables, that is, the X-ray emission, the thermal
Sunyaev-Zel'dovich (SZ) signal, the velocity dispersion of the cluster
galaxies, and gravitational lensing, the gravitational potential of galaxy
clusters can be jointly reconstructed. We derive the two main ingredients
required for this joint reconstruction: the potentials individually
reconstructed from the observables and their covariance matrices, which act as
a weight in the joint reconstruction. We show here the method to derive these
quantities. The result of the joint reconstruction applied to a real cluster
will be discussed in a forthcoming paper. We apply the Richardson-Lucy
deprojection algorithm to data on a two-dimensional (2D) grid. We first test
the 2D deprojection algorithm on a -profile. Assuming hydrostatic
equilibrium, we further reconstruct the gravitational potential of a simulated
galaxy cluster based on synthetic SZ and X-ray data. We then reconstruct the
projected gravitational potential of the massive and dynamically active cluster
Abell 2142, based on the X-ray observations collected with XMM-Newton and the
SZ observations from the Planck satellite. Finally, we compute the covariance
matrix of the projected reconstructed potential of the cluster Abell 2142 based
on the X-ray measurements collected with XMM-Newton. The gravitational
potentials of the simulated cluster recovered from synthetic X-ray and SZ data
are consistent, even though the potential reconstructed from X-rays shows
larger deviations from the true potential. Regarding Abell 2142, the projected
gravitational cluster potentials recovered from SZ and X-ray data reproduce
well the projected potential inferred from gravitational-lensing observations.
(abridged)Comment: accepted for publication in the journal A&
Blubber Transciptome Response to Acute Stress Axis Activation Involves Transient Charges in Adipogenesis and Lipolysis in Fast-Adapted Marine Mammal
Stress can compromise an animal\u27s ability to conserve metabolic stores and participate in energy-demanding activities that are critical for fitness. Understanding how wild animals, especially those already experiencing physiological extremes (e.g. fasting), regulate stress responses is critical for evaluating the impacts of anthropogenic disturbance on physiology and fitness, key challenges for conservation. However, studies of stress in wildlife are often limited to baseline endocrine measurements and few have investigated stress effects in fasting-adapted species. We examined downstream molecular consequences of hypothalamic-pituitary-adrenal (HPA) axis activation by exogenous adrenocorticotropic hormone (ACTH) in blubber of northern elephant seals due to the ease of blubber sampling and its key role in metabolic regulation in marine mammals. We report the first phocid blubber transcriptome produced by RNAseq, containing over 140,000 annotated transcripts, including metabolic and adipocytokine genes of interest. The acute response of blubber to stress axis activation, measured 2 hours after ACTH administration, involved highly specific, transient (lasting \u3c24 \u3ehours) induction of gene networks that promote lipolysis and adipogenesis in mammalian adipocytes. Differentially expressed genes included key adipogenesis factors which can be used as blubber-specific markers of acute stress in marine mammals of concern for which sampling of other tissues is not possible
A dinâmica socioeconômica das comunidades rurais amazônicas: o caso da Comunidade de Nossa Senhora do Rosário - Parintins - AM.
O presente trabalho visa contribuir na construção de parâmetros que sirvam de base para a introdução de tecnologias adequadas em comunidades rurais amazônicas, considerando a estrutura social e agrária, bem como a produção e a organização, com a finalidade de compreender melhor as realidades locais
The strongest gravitational lenses: II. Is the large Einstein radius of MACS J0717.5+3745 in conflict with LCDM?
Can the standard cosmological model be questioned on the basis of a single
observed extreme galaxy cluster? Usually, the word extreme refers directly to
cluster mass, which is not a direct observable and thus subject to substantial
uncertainty. Hence, it is desirable to extend studies of extreme clusters to
direct observables, such as the Einstein radius (ER). We aim to evaluate the
occurrence probability of the large observed ER of MACS J0717.5 within the
standard LCDM cosmology. In particular, we want to model the distribution
function of the single largest ER in a given cosmological volume and to study
which underlying assumptions and effects have the strongest impact on the
results. We obtain this distribution by a Monte Carlo approach, based on the
semi-analytic modelling of the halo population on the past lightcone. After
sampling the distribution, we fit the results with the general extreme value
(GEV) distribution which we use for the subsequent analysis. We find that the
distribution of the maximum ER is particularly sensitive to the precise choice
of the halo mass function, lens triaxiality, the inner slope of the halo
density profile and the mass-concentration relation. Using the distributions so
obtained,we study the occurrence probability of the large ER of MACS J0717.5,
finding that this system is not in tension with LCDM. We also find that the GEV
distribution can be used to fit very accurately the sampled distributions and
that all of them can be described by a Frechet distribution. With a multitude
of effects that strongly influence the distribution of the single largest ER,
it is more than doubtful that the standard LCDM cosmology can be ruled out on
the basis of a single observation. If, despite the large uncertainties in the
underlying assumptions, one wanted to do so, a much larger ER (> 100 arcsec)
than that of MACS J0717.5 would have to be observed.Comment: 15 pages, 11 figures, accepted for publication in Astronomy and
Astrophysics, minor corrections to match the accepted version, added
discussion of the distribution of the largest Einstein radii for the MACS
survey area, extended Fig.
Análise de redes sociais como instrumento de compreensão da dinâmica organizativa de uma comunidade rural no Amazonas.
O texto apresenta uma análise das relações sociais que se estabelecem na comunidade do Lago do Santana, localizada no MunicĂpio de Manacapuru, AM, como estratĂ©gia de superação de problemas individuais e coletivos da comunidade. É um estudo que utiliza como base de análise as redes sociais dessa comunidade. Buscou-se entender como ela está organizada, como se relaciona e quais dinâmicas estĂŁo presentes e sĂŁo capazes de impulsionar a resolução de problemas, garantindo avanços individuais e coletivos. Foram analisados aspectos como: faixa etária, nĂvel de escolaridade e infraestrutura da comunidade. No âmbito da estrutura econĂ´mica, analisaram-se as questões pertinentes Ă s relações do trabalho e o estabelecimento da relação de ajuda mĂştua. O objetivo da pesquisa foi entender e mensurar a forma como a comunidade estabelece relações e define estratĂ©gias para o viver bem, desenvolvendo a agricultura e utilizando seus recursos naturais, a terra, a floresta e a água
A PCA-based automated finder for galaxy-scale strong lenses
We present an algorithm using Principal Component Analysis (PCA) to subtract
galaxies from imaging data, and also two algorithms to find strong,
galaxy-scale gravitational lenses in the resulting residual image. The combined
method is optimized to find full or partial Einstein rings. Starting from a
pre-selection of potential massive galaxies, we first perform a PCA to build a
set of basis vectors. The galaxy images are reconstructed using the PCA basis
and subtracted from the data. We then filter the residual image with two
different methods. The first uses a curvelet (curved wavelets) filter of the
residual images to enhance any curved/ring feature. The resulting image is
transformed in polar coordinates, centered on the lens galaxy center. In these
coordinates, a ring is turned into a line, allowing us to detect very faint
rings by taking advantage of the integrated signal-to-noise in the ring (a line
in polar coordinates). The second way of analysing the PCA-subtracted images
identifies structures in the residual images and assesses whether they are
lensed images according to their orientation, multiplicity and elongation. We
apply the two methods to a sample of simulated Einstein rings, as they would be
observed with the ESA Euclid satellite in the VIS band. The polar coordinates
transform allows us to reach a completeness of 90% and a purity of 86%, as soon
as the signal-to-noise integrated in the ring is higher than 30, and almost
independent of the size of the Einstein ring. Finally, we show with real data
that our PCA-based galaxy subtraction scheme performs better than traditional
subtraction based on model fitting to the data. Our algorithm can be developed
and improved further using machine learning and dictionary learning methods,
which would extend the capabilities of the method to more complex and diverse
galaxy shapes
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