842 research outputs found
Massive Star cluster formation under the microscope at z=6
We report on a superdense star-forming region with an effective radius (R_e)
smaller than 13 pc identified at z=6.143 and showing a star-formation rate
density \Sigma_SFR~1000 Msun/yr/kpc2 (or conservatively >300 Msun/yr/kpc2).
Such a dense region is detected with S/N>40 hosted by a dwarf extending over
440 pc, dubbed D1 (Vanzella et al. 2017b). D1 is magnified by a factor
17.4+/-5.0 behind the Hubble Frontier Field galaxy cluster MACS~J0416 and
elongated tangentially by a factor 13.2+/-4.0 (including the systematic
errors). The lens model accurately reproduces the positions of the confirmed
multiple images with a r.m.s. of 0.35", and the tangential stretch is well
depicted by a giant multiply-imaged Lya arc. D1 is part of an interacting
star-forming complex extending over 800 pc. The SED-fitting, the very blue
ultraviolet slope (\beta ~ -2.5, F(\lambda) ~ \lambda^\beta) and the prominent
Lya emission of the stellar complex imply that very young (< 10-100 Myr),
moderately dust-attenuated (E(B-V)<0.15) stellar populations are present and
organised in dense subcomponents. We argue that D1 (with a stellar mass of 2 x
10^7 Msun) might contain a young massive star cluster of M < 10^6 Msun and
Muv~-15.6 (or m_uv=31.1), confined within a region of 13 pc, and not dissimilar
from some local super star clusters (SSCs). The ultraviolet appearance of D1 is
also consistent with a simulated local dwarf hosting a SSC placed at z=6 and
lensed back to the observer. This compact system fits into some popular
globular cluster formation scenarios. We show that future high spatial
resolution imaging (e.g., E-ELT/MAORY-MICADO and VLT/MAVIS) will allow us to
spatially resolve light profiles of 2-8 pc.Comment: 21 pages, 14 figures, 1 table, MNRAS accepte
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
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
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
Ionising the Intergalactic Medium by Star Clusters: The first empirical evidence
We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting
galaxy 'Ion2' at z=3.2121 and compare it to that of the recently discovered
strongly lensed LyC-emitter at z=2.37, known as the 'Sunburst' arc. Three main
results emerge from the X-Shooter spectrum: (a) the Lya has three distinct
peaks with the central one at the systemic redshift, indicating a ionised
tunnel through which both Lya and LyC radiation escape; (b) the large O32
oxygen index ([OIII]4959-5007 / [OII]3727-3729) of 9.18(-1.32/+1.82) is
compatible to those measured in local (z~0.4) LyC leakers; (c) there are narrow
nebular high-ionisation metal lines with \sigma_v < 20 km/s, which confirms the
presence of young hot, massive stars. The HeII1640 appears broad, consistent
with a young stellar component including Wolf-Rayet stars. Similarly, the
Sunburst LyC-emitter shows a triple-peaked Lya profile and from VLT/MUSE
spectroscopy the presence of spectral features arising from young hot and
massive stars. The strong lensing magnification, (\mu > 20), suggests that this
exceptional object is a gravitationally-bound star cluster observed at a
cosmological distance, with a stellar mass M <~ 10^7 Msun and an effective
radius smaller than 20 pc. Intriguingly, sources like Sunburst but without
lensing magnification might appear as Ion2-like galaxies, in which unresolved
massive star clusters dominate the ultraviolet emission. This work supports the
idea that dense young star clusters can contribute to the ionisation of the IGM
through holes created by stellar feedback.Comment: 13 pages, 9 figures and 1 table, MNRAS accepted. Some typos fixe
Reflexões sobre agricultura familiar, inovação e desenvolvimento na Amazônia.
O texto apresenta algumas reflexões sobre o ecossistema amazĂ´nico no seu aspecto fĂsico, de exploração e da fragilidade desse ambiente quando se trata de uso dos recursos naturais. Traz para a discussĂŁo aspectos da diversidade biolĂłgica e sociocultural, bem como os efeitos das polĂticas governamentais sobre esse ambiente. Enfatiza e caracteriza a agricultura familiar amazĂ´nica e suas relações com o ambiente. Analisa a importância dos saberes locais no processo de geração e transferĂŞncia de tecnologias e a importância de se juntar esses saberes com os conhecimentos cientĂficos. A conjunção dos conhecimentos gera tecnologias adequadas ao ambiente, as quais, por sua vez, geram inovação e desenvolvimento. A participação das pessoas Ă© importante para que ocorra a inovação. Neste aspecto, buscam-se, cada vez mais, metodologias que permitam analisar e inserir as pessoas nos processos de desenvolvimento
Direct Lyman continuum and Lyman-alpha escape observed at redshift 4
We report on the serendipitous discovery of a z=4.0, M1500=-22.20
star-forming galaxy (Ion3) showing copious Lyman continuum (LyC) leakage (~60%
escaping), a remarkable multiple peaked Lya emission, and significant Lya
radiation directly emerging at the resonance frequency. This is the highest
redshift confirmed LyC emitter in which the ionising and Lya radiation possibly
share a common ionised cavity (with N_HI<10^17.2 cm^-2). Ion3 is spatially
resolved, it shows clear stellar winds signatures like the P-Cygni NV1240
profile, and has blue ultraviolet continuum (\beta = -2.5 +/- 0.25, F_\lambda~
\lambda^\beta) with weak low-ionisation interstellar metal lines. Deep
VLT/HAWKI Ks and Spitzer/IRAC 3.6um and 4.5um imaging show a clear photometric
signature of the Halpha line with equivalent width of 1000A rest-frame emerging
over a flat continuum (Ks-4.5um ~ 0). From the SED fitting we derive a stellar
mass of 1.5x10^9 Msun, SFR of 140 Msun/yr and age of ~10 Myr, with a low dust
extinction, E(B-V)< 0.1, placing the source in the starburst region of the
SFR-M^* plane. Ion3 shows similar properties of another LyC emitter previously
discovered (z=3.21, Ion2, Vanzella et al. 2016). Ion3 (and Ion2) represents
ideal high-redshift reference cases to guide the search for reionising sources
at z>6.5 with JWST.Comment: Accepted for publication in MNRAS. 5 pages, 4 figures, 1 tabl
Effects of cluster galaxies on arc statistics
We present the results of a set of numerical simulations evaluating the
effect of cluster galaxies on arc statistics. We perform a first set of
gravitational lensing simulations using three independent projections for each
of nine different galaxy clusters obtained from N-body simulations. The
simulated clusters consist of dark matter only. We add a population of galaxies
to each cluster, mimicking the observed luminosity function and the spatial
galaxy distribution, and repeat the lensing simulations including the effects
of cluster galaxies, which themselves act as individual lenses. Each galaxy is
represented by a spherical Navarro, Frenk & White (1997) density profile. We
consider the statistical distributions of the properties of the gravitational
arcs produced by our clusters with and without galaxies. We find that the
cluster galaxies do not introduce perturbations strong enough to significantly
change the number of arcs and the distributions of lengths, widths, curvature
radii and length-to-width ratios of long arcs. We find some changes to the
distribution of short-arc properties in presence of cluster galaxies. The
differences appear in the distribution of curvature radii for arc lengths
smaller than 12'', while the distributions of lengths, widths and
length-to-width ratios are significantly changed only for arcs shorter than
4''.Comment: 11 pages, Latex using MN style, 6 figures enclosed. Version accepted
for publication in MNRAS. Gzipped file including a full resolution version of
Figures 2a, 2b, 3a, 3b, 3c can be downloaded by anonymous ftp at
http://gt.pd.astro.it/~bepi/PAPERS/lensing.ps.g
Shedding X-ray Light on the Role of Magnesium in the Activity of Mycobacterium tuberculosis Salicylate Synthase (MbtI) for Drug Design
The Mg2+-dependent Mycobacterium tuberculosis salicylate synthase (MbtI) is a key enzyme involved in the biosynthesis of siderophores. Because iron is essential for the survival and pathogenicity of the microorganism, this protein constitutes an attractive target for antitubercular therapy, also considering the absence of homologous enzymes in mammals. An extension of the structure-activity relationships of our furan-based candidates allowed us to disclose the most potent competitive inhibitor known to date (10, Ki = 4 ÎĽM), which also proved effective on mycobacterial cultures. By structural studies, we characterized its unexpected Mg2+-independent binding mode. We also investigated the role of the Mg2+ cofactor in catalysis, analyzing the first crystal structure of the MbtI-Mg2+-salicylate ternary complex. Overall, these results pave the way for the development of novel antituberculars through the rational design of improved MbtI inhibitors
The Frontier Fields Lens Modeling Comparison Project
Gravitational lensing by clusters of galaxies offers a powerful probe of
their structure and mass distribution. Deriving a lens magnification map for a
galaxy cluster is a classic inversion problem and many methods have been
developed over the past two decades to solve it. Several research groups have
developed techniques independently to map the predominantly dark matter
distribution in cluster lenses. While these methods have all provided
remarkably high precision mass maps, particularly with exquisite imaging data
from the Hubble Space Telescope (HST), the reconstructions themselves have
never been directly compared. In this paper, we report the results of comparing
various independent lens modeling techniques employed by individual research
groups in the community. Here we present for the first time a detailed and
robust comparison of methodologies for fidelity, accuracy and precision. For
this collaborative exercise, the lens modeling community was provided simulated
cluster images -- of two clusters Ares and Hera -- that mimic the depth and
resolution of the ongoing HST Frontier Fields. The results of the submitted
reconstructions with the un-blinded true mass profile of these two clusters are
presented here. Parametric, free-form and hybrid techniques have been deployed
by the participating groups and we detail the strengths and trade-offs in
accuracy and systematics that arise for each methodology. We note in conclusion
that lensing reconstruction methods produce reliable mass distributions that
enable the use of clusters as extremely valuable astrophysical laboratories and
cosmological probes.Comment: 38 pages, 25 figures, submitted to MNRAS, version with full
resolution images can be found at
http://pico.bo.astro.it/~massimo/papers/FFsims.pd
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