5,224 research outputs found
ZEN2: A narrow J-band search for z~9 Lya emitting galaxies directed towards three lensing clusters
We present the results of a continuing survey to detect Lya emitting galaxies
at redshifts z~9: the ZEN ("z equals nine'') survey. We have obtained deep
VLT/ISAAC observations in the narrow J-band filter NB119 directed towards three
massive lensing clusters: Abell clusters 1689, 1835, and 114. The foreground
clusters provide a magnified view of the distant universe and permit a
sensitive test for the presence of very high-redshift galaxies. We search for
z~9 Lya emitting galaxies displaying a significant narrow-band excess relative
to accompanying J-band observations that remain undetected in HST/ACS optical
images of each field. No sources consistent with this criterion are detected
above the unlensed 90% point-source flux limit of the narrow-band image,
F_NB=3.7e-18 ergs/s/cm2. To date, the total coverage of the ZEN survey has
sampled a volume at z~9 of approximately 1700 co-moving Mpc3 to a Lya emission
luminosity of 1e43 erg/s. We conclude by considering the prospects for
detecting z~9 Lya emitting galaxies in light of both observed galaxy properties
at z7.Comment: 7 pages, MNRAS accepte
Limits on the luminosity function of Ly-alpha emitters at z = 7.7
The Ly-alpha luminosity function (LF) of high-redshift Ly-alpha emitters
(LAEs) is one of the few observables of the re-ionization epoch accessible to
date with 8-10 m class telescopes. The evolution with redshift allows one to
constrain the evolution of LAEs and their role in re-ionizing the Universe at
the end of the Dark Ages.
We have performed a narrow-band imaging program at 1.06 microns at the CFHT,
targeting Ly-alpha emitters at redshift z ~ 7.7 in the CFHT-LS D1 field. From
these observations we have derived a photometric sample of 7 LAE candidates at
z ~ 7.7.
We derive luminosity functions for the full sample of seven objects and for
sub-samples of four objects. If the brightest objects in our sample are real,
we infer a luminosity function which would be difficult to reconcile with
previous work at lower redshift. More definitive conclusions will require
spectroscopic confirmation.Comment: 12 pages, accepted to Astronomy and Astrophysic
Dynamic nozzles for drop generators
received: 2015-06-03 accepted: 2015-10-16 published: 2015-11-03received: 2015-06-03 accepted: 2015-10-16 published: 2015-11-03This work was funded by the UK Engineering and Physical Sciences Research Council (Grant No. EP/H018913/1), the John Fell Oxford University Press Research Fund, and the Royal Society
Comparison of eta and eta' production in the pp -> pp eta(eta') reactions near threshold
The total cross section of the pp -> pp eta' reaction has been measured at
two energies near threshold by detecting the final protons in a magnetic
spectrometer. The values obtained are about a factor of 70 less than for the
corresponding eta production, in good agreement with the predictions of a
one-pion-exchange model.Comment: 10 pages, Latex with 3 eps figure
RÉACTION DE PRODUCTION DE PIONS PRÈS DU SEUIL
La distribution angulaire de la section efficace différentielle de la réaction 40Ca(p, π+)41Ca (état fondamental) a été mesurée. L'étude de la dépendance en énergie de la production de pions près du seuil a été faite à transfert de moment constant. La section efficace décroît d'un facteur 7 pour des énergies de protons variant de 154 à 149 MeV (Eπ varie de 17,4 à 12,4 MeV). L'interprétation des résultats est faite dans le cadre d'un mécanisme à un nucléon
Deconstructing density: strategic dilemmas confronting the post-Apartheid city
Public authorities in many countries around the world are seeking to raise urban densities. Residential densification is particularly important in South Africa because of the colonial and apartheid legacy of sprawling, fragmented, racially divided cities. The paper examines the case for densifying central Cape Town and provides a framework to help deconstruct the concept and explore the policy challenges faced. It focuses on the bold aim to treble the area’s population within 10 years, and identifies issues where further consideration and public debate are required for how this can be achieved in a way that is desirable, affordable and fair. A key message is the need to understand both the composition of demand for central city living and the challenges involved in supplying suitable housing and amenities at higher densities. The level of social inequality in the city poses greater complications than elsewhere
A narrow-band search for Ly alpha emitting galaxies at z = 8.8
Aims: The first star forming galaxies in the early universe should be copious
Ly alpha emitters, and may play a significant role in ionizing the
intergalactic medium (IGM). It has been proposed that the luminosity function
of Lya emitting galaxies beyond z~6 may be used to constrain the neutral
fraction of the IGM during this epoch. In this work we report on a search for
Ly alpha emitters at redshift 8.8.
Methods: We performed a narrow band imaging programme using ISAAC at the ESO
VLT. Seven fields, covering a total area of 31sq. arcmin and for which optical
and broad band infra-red images have been obtained in the GOODS survey, were
imaged to a limiting flux (respectively luminosity) of ~ 1.3 x 10^{-17}
ergs.s^{-1}.cm^{-2} (respectively ~ 1.3 x 10^{43} ergs.s^{-1} in a narrow band
filter centered in a region of low OH sky emission at 1.19 micron. Candidate
Lyman alpha emitters are objects that are detected in the ISAAC NB images and
undetected in the visible broad band images.
Results: No z=8.8 Ly alpha emitting galaxies were detected to a limit
approaching recent estimates of the luminosity function at z ~ 6. Our results
do suggest, however, that detections or substantial constraints could be
achieved by this method in the near future with larger field instruments
planned for various telescopes.Comment: 7 pages, accepted for publication in A&
Near-Threshold Production of omega Mesons in the pp -> pp omega Reaction
The total cross section for omega production in the pp -> pp omega reaction
has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy
dependence is easily understood in terms of a strong proton-proton final state
interaction combined with a smearing over the width of the state. The ratio of
near-threshold phi and omega production is consistent with the predictions of a
one-pion-exchange model and the degree of violation of the OZI rule is similar
to that found in the pi-p -> n omega/phi reactions.Comment: Report in LaTeX2e. 12 pages with 2 eps figure
Structure detection in the D1 CFHTLS deep field using accurate photometric redshifts: a benchmark
We investigate structures in the D1 CFHTLS deep field in order to test the
method that will be applied to generate homogeneous samples of clusters and
groups of galaxies in order to constrain cosmology and detailed physics of
groups and clusters. Adaptive kernel technique is applied on galaxy catalogues.
This technique needs none of the usual a-priori assumptions (luminosity
function, density profile, colour of galaxies) made with other methods. Its
main drawback (decrease of efficiency with increasing background) is overcame
by the use of narrow slices in photometric redshift space. There are two main
concerns in structure detection. One is false detection and the second, the
evaluation of the selection function in particular if one wants "complete"
samples. We deal here with the first concern using random distributions. For
the second, comparison with detailed simulations is foreseen but we use here a
pragmatic approach with comparing our results to GalICS simulations to check
that our detection number is not totally at odds compared to cosmological
simulations. We use XMM-LSS survey and secured VVDS redshifts up to z~1 to
check individual detections. We show that our detection method is basically
capable to recover (in the regions in common) 100% of the C1 XMM-LSS X-ray
detections in the correct redshift range plus several other candidates.
Moreover when spectroscopic data are available, we confirm our detections, even
those without X-ray data.Comment: 14 pages, 22 additionnal jpeg figures, accepted in A&
Evidence for Transgenerational Transmission of Epigenetic Tumor Susceptibility in Drosophila
Transgenerational epigenetic inheritance results from incomplete erasure of parental epigenetic marks during epigenetic reprogramming at fertilization. The significance of this phenomenon, and the mechanism by which it occurs, remains obscure. Here, we show that genetic mutations in Drosophila may cause epigenetic alterations that, when inherited, influence tumor susceptibility of the offspring. We found that many of the mutations that affected tumorigenesis induced by a hyperactive JAK kinase, HopTum-l, also modified the tumor phenotype epigenetically, such that the modification persisted even in the offspring that did not inherit the modifier mutation. We analyzed mutations of the transcription repressor Krüppel (Kr), which is one of the hopTum-l enhancers known to affect ftz transcription. We demonstrate that the Kr mutation causes increased DNA methylation in the ftz promoter region, and that the aberrant ftz transcription and promoter methylation are both transgenerationally heritable if HopTum-l is present in the oocyte. These results suggest that genetic mutations may alter epigenetic markings in the form of DNA methylation, which are normally erased early in the next generation, and that JAK overactivation disrupts epigenetic reprogramming and allows inheritance of epimutations that influence tumorigenesis in future generations
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