576 research outputs found
Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data
About two-thirds of present-day, large galaxies are spirals such as the Milky
Way or Andromeda, but the way their thin rotating disks formed remains
uncertain. Observations have revealed that half of their progenitors, six
billion years ago, had peculiar morphologies and/or kinematics, which exclude
them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of
similar mass, are found to be the likeliest driver for such strong
peculiarities. However, thin disks are fragile and easily destroyed by such
violent collisions, which creates a critical tension between the observed
fraction of thin disks and their survival within the L-CDM paradigm. Here we
show that the observed high occurrence of mergers amongst their progenitors is
only apparent and is resolved when using morpho-kinematic observations which
are sensitive to all the phases of the merging process. This provides an
original way of narrowing down observational estimates of the galaxy merger
rate and leads to a perfect match with predictions by state-of-the-art L-CDM
semi-empirical models with no particular fine-tuning needed. These results
imply that half of local thin disks do not survive but are actually rebuilt
after a gas-rich major merger occurring in the past nine billion years, i.e.,
two-thirds of the lifetime of the Universe. This emphasizes the need to study
how thin disks can form in halos with a more active merger history than
previously considered, and to investigate what is the origin of the gas
reservoir from which local disks would reform.Comment: 19 pages, 7 figures, 2 tables. Accepted in ApJ. V2 to match proof
corrections and added reference
Pre-biopsy MRI as an adjunct for cancer detection in men with elevated PSA and no previous biopsy
The role of magnetic resonance imaging (MRI) prior to biopsy in the diagnosis of prostate cancer in biopsy-naïve patients has been strengthened by recent developments such as the PIRADS V2 criteria, which cover acquisition, interpretation, and reporting for clinical practice and data collection for research. Important questions on the role of prostate MRI remain: can MRI be used as a triage test before first biopsy series? Can it be used to avoid the use of systematic biopsies (SB) and instead use only targeted biopsies (TB) to MRI-suspicious lesions? Studies to evaluate image guided TB compared to SB have started to accumulate. Objectives of these studies should be to reduce the detection of clinically insignificant disease, to maximize the detection of clinically significant cancer (CSC), to better assess disease size, grade and location. Accurate diagnosis will allow the choice of the most appropriate treatments options, minimising side effects and reducing overtreatment. Study results on MRI-TB detection rates are promising however some limitations should be considered. The majority of published and ongoing studies have been performed at expert centres, in order to demonstrate the optimal performance of MRI. Then, the validation of this strategy in less specialised institutions will be necessary before incorporating recommendations in international guidelines. It necessitates training for radiologists and urologists to perform and read MRI and MRI-targeted biopsy through education programs and standardization tools. All these advances will be consolidated with expected genetic screening tools to improve the detection of aggressive cancer
Performance study of ground-based infrared Bracewell interferometers - Application to the detection of exozodiacal dust disks with GENIE
Nulling interferometry, a powerful technique for high-resolution imaging of
the close neighbourhood of bright astrophysical objets, is currently considered
for future space missions such as Darwin or the Terrestrial Planet Finder
Interferometer (TPF-I), both aiming at Earth-like planet detection and
characterization. Ground-based nulling interferometers are being studied for
both technology demonstration and scientific preparation of the Darwin/TPF-I
missions through a systematic survey of circumstellar dust disks around nearby
stars. In this paper, we investigate the influence of atmospheric turbulence on
the performance of ground-based nulling instruments, and deduce the major
design guidelines for such instruments. End-to-end numerical simulations allow
us to estimate the performance of the main subsystems and thereby the actual
sensitivity of the nuller to faint exozodiacal disks. Particular attention is
also given to the important question of stellar leakage calibration. This study
is illustrated in the context of GENIE, the Ground-based European Nulling
Interferometer Experiment, to be installed at the VLTI and working in the L'
band. We estimate that this instrument will detect exozodiacal clouds as faint
as about 50 times the Solar zodiacal cloud, thereby placing strong constraints
on the acceptable targets for Darwin/TPF-I.Comment: A&A, accepte
A temperature-controlled device for volumetric measurements of Helium adsorption in porous media
We describe a set-up for studying adsorption of helium in silica aerogels,
where the adsorbed amount is easily and precisely controlled by varying the
temperature of a gas reservoir between 80 K and 180 K. We present validation
experiments and a first application to aerogels. This device is well adapted to
study hysteresis, relaxation, and metastable states in the adsorption and
desorption of fluids in porous media
531 new spectroscopic redshifts from the CDFS and a test on the cosmological relevance of the GOODS-South field
(Abbrev.) This paper prepares a series of papers analysing the Intermediate
MAss Galaxy Evolution Sequence (IMAGES) up to z=1. Intermediate mass galaxies
(MJ <=-20.3) are selected from the Chandra Deep Field South (CDFS) for which we
identify a serious lack of spectroscopically determined redshifts..... We have
spectroscopically identified 691 objects including 580 gal., 7 QSOs, and 104
stars. This study provides 531 new redshifts in the CDFS. It confirms the
presence of several large scale structures in the CDFS. To test the impact of
these structures in the GOODS-South field, we ... compare the evolution of
rest-frame U, B, V and K galaxy luminosity densities to that derived from the
CFRS. The CDFS field shows a significant excess of luminosity densities in the
z=0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex
at 2.1 um. Stellar mass and specific star formation evolutions might be
significantly affected by the presence of the peculiar large scale structures
at z= 0.668 and at z= 0.735, that contain a significant excess of evolved,
massive galaxies when compared to other fields. This leads to a clear warning
to results based on the CDFS/GOODS South fields, especially those related to
the evolution of red luminosity densities, i.e. stellar mass density and
specific star formation rate. Photometric redshift techniques, when applied to
that field, are producing quantities which are apparently less affected by
cosmic variance (0.25 dex at 2.1 um), however at the cost of the difficulty in
disentangling between evolutionary and cosmic variance effects.Comment: Accepted for publication in A&A, 19 pages, 13 figure
Molecular nature of breakdown of the folic acid under hydrothermal treatment: a combined experimental and DFT study
Using a combination of experimental Raman, FTIR, UV–VIS absorption and emission data, together with the corresponding DFT calculations we propose the mechanism of modification of the folic acid specifically under the hydrothermal treatment at 200 °C. We established that folic acid breaks down into fragments while the pteridine moiety remains intact likely evolving into 6-formylpterin with the latter responsible for the increase in fluorescence emission at 450 nm. The results suggest that hydrothermal approach can be used for production of other purpose-engineered fluorophores
The E-ELT Multi-Object Spectrograph: latest news from MOSAIC
There are 8000 galaxies, including 1600 at z larger than 1.6, which could be
simultaneously observed in an E-ELT field of view of 40 sq. arcmin. A
considerable fraction of astrophysical discoveries require large statistical
samples, which can only be obtained with multi-object spectrographs (MOS).
MOSAIC will provide a vast discovery space, enabled by a multiplex of 200 and
spectral resolving powers of R=5000 and 20000. MOSAIC will also offer the
unique capability of more than 10 "high-definition" (multi-object adaptive
optics, MOAO) integral-field units, optimised to investigate the physics of the
sources of reionization. The combination of these modes will make MOSAIC the
world-leading MOS facility, contributing to all fields of contemporary
astronomy, from extra-solar planets, to the study of the halo of the Milky Way
and its satellites, and from resolved stellar populations in nearby galaxies
out to observations of the earliest "first-light" structures in the Universe.
It will also study the distribution of the dark and ordinary matter at all
scales and epochs of the Universe. Recent studies of critical technical issues
such as sky-background subtraction and MOAO have demonstrated that such a MOS
is feasible with state-of-the-art technology and techniques. Current studies of
the MOSAIC team include further trade-offs on the wavelength coverage, a
solution for compensating for the non-telecentric new design of the telescope,
and tests of the saturation of skylines especially in the near-IR bands. In the
2020s the E-ELT will become the world's largest optical/IR telescope, and we
argue that it has to be equipped as soon as possible with a MOS to provide the
most efficient, and likely the best way to follow-up on James Webb Space
Telescope (JWST) observations.Comment: 10 pages, 3 Figures, in Ground-based and Airborne Instrumentation for
Astronomy VI, 2016, Proc. SPI
Evidence for a disorder driven phase transition in the condensation of 4He in aerogels
We report on thermodynamic and optical measurements of the condensation
process of He in three silica aerogels of different microstructures. For
the two base-catalysed aerogels, the temperature dependence of the shape of
adsorption isotherms and of the morphology of the condensation process show
evidence of a disorder driven transition, in agreement with recent theoretical
predictions. This transition is not observed for a neutral-catalysed aerogel,
which we interpret as due to a larger disorder in this case.Comment: 11 page
IMAGES I. Strong evolution of galaxy kinematics since z=1
(abbreviated) We present the first results of the ESO large program,
``IMAGES'' which aims at obtaining robust measurements of the kinematics of
distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D
spectroscopy is essential to robustly measure the often distorted kinematics of
distant galaxies (e.g., Flores et al. 2006). We derive the velocity fields and
-maps of 36 galaxies at 0.4<z<0.75 from the kinematics of the [OII]
emission line doublet, and generate a robust technique to identify the nature
of the velocity fields based on the pixels of the highest signal-to-noise
ratios (S/N). We have gathered a unique sample of 63 velocity fields of
emission line galaxies (W0([OII]) > 15 A) at z=0.4-0.75, which are a
representative subsample of the population of M_stellar>1.5x10^{10} M_sun
emission line galaxies in this redshift range, and are largely unaffected by
cosmic variance. Taking into account all galaxies -with or without emission
lines- in that redshift range, we find that at least 41+/-7% of them have
anomalous kinematics, i.e., they are not dynamically relaxed. This includes
26+/-7% of distant galaxies with complex kinematics, i.e., they are not simply
pressure or rotationally supported. Our result implies that galaxy kinematics
are among the most rapidly evolving properties, because locally, only a few
percent of the galaxies in this mass range have complex kinematics.Comment: 17 pages, 6 figures, Accepted by A&
EAGLE multi-object AO concept study for the E-ELT
EAGLE is the multi-object, spatially-resolved, near-IR spectrograph
instrument concept for the E-ELT, relying on a distributed Adaptive Optics,
so-called Multi Object Adaptive Optics. This paper presents the results of a
phase A study. Using 84x84 actuator deformable mirrors, the performed analysis
demonstrates that 6 laser guide stars and up to 5 natural guide stars of
magnitude R<17, picked-up in a 7.3' diameter patrol field of view, allow us to
obtain an overall performance in terms of Ensquared Energy of 35% in a 75x75
mas^2 spaxel at H band, whatever the target direction in the centred 5' science
field for median seeing conditions. The computed sky coverage at galactic
latitudes |b|~60 is close to 90%.Comment: 6 pages, to appear in the proceedings of the AO4ELT conference, held
in Paris, 22-26 June 200
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