5,729 research outputs found
Newly Discovered Bright z~9-10 Galaxies and Improved Constraints on Their Prevalence Using the Full CANDELS Area
We report the results of an expanded search for z~9-10 candidates over the
~883 arcmin^2 CANDELS+ERS fields. This study adds 147 arcmin^2 to the search
area we consider over the CANDELS COSMOS, UDS, and EGS fields, while expanding
our selection to include sources with bluer J_{125}-H_{160} colors than our
previous J_{125}-H_{160}>0.5 mag selection. In searching for new z~9-10
candidates, we make full use of all available HST, Spitzer/IRAC, and
ground-based imaging data. As a result of our expanded search and use of
broader color criteria, 3 new candidate z~9-10 galaxies are identified. We also
find again the z=8.683 source previously confirmed by Zitrin+2015. This brings
our sample of probable z~9-11 galaxy candidates over the CANDELS+ERS fields to
19 sources in total, equivalent to 1 candidate per 47 arcmin^2 (1 per 10
WFC3/IR fields). To be comprehensive, we also discuss 28 mostly lower
likelihood z~9-10 candidates, including some sources that seem to be reliably
at z>8 using the HST+IRAC data alone, but which the ground-based data show are
much more likely at z<4. One case example is a bright z~9.4 candidate COS910-8
which seems instead to be at z~2. Based on this expanded sample, we obtain a
more robust LF at z~9 and improved constraints on the volume density of bright
z~9 and z~10 galaxies. Our improved z~9-10 results again reinforce previous
findings for strong evolution in the UV LF at z>8, with a factor of ~10
evolution seen in the luminosity density from z~10 to z~8.Comment: 22 pages, 12 figures, 6 tables, accepted for publication in the
Astrophysical Journa
Fifty years of thoracic surgical research in South Africa
Aim. To investigate the scope and trends in clinical research inSouth African thoracic surgery between 1955 and 2006 and tomeasure its impact on clinical practice.Method. A systematic review of all SA thoracic surgicalpublications was performed.Results. There were 252 general thoracic publications and amarked decrease in publications was noted after the peakperiod of productivity of the 1980s. There was a shift towardthe private sector as an origin of articles and toward a local,non-indexed journal. Inflammatory lung disease was themost frequent topic of publication. Case series and casereports were the most frequent type of article.Conclusion. The vulnerability of a small specialty in adeveloping country is illustrated by the clear trends thatemerged. The study provides important indicators for futureresearch, highlights the need for a national database of clinicalexperience, and emphasises the importance of rekindlinginterest and a culture of research in thoracic surgery
The GREATS H+[OIII] Luminosity Function and Galaxy Properties at : Walking the Way of JWST
The James Webb Space Telescope will allow to spectroscopically study an
unprecedented number of galaxies deep into the reionization era, notably by
detecting [OIII] and H nebular emission lines. To efficiently prepare
such observations, we photometrically select a large sample of galaxies at
and study their rest-frame optical emission lines. Combining data from
the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and
from HST, we perform spectral energy distribution (SED) fitting, using
synthetic SEDs from a large grid of photoionization models. The deep
Spitzer/IRAC data combined with our models exploring a large parameter space
enables to constrain the [OIII]+H fluxes and equivalent widths for our
sample, as well as the average physical properties of galaxies, such
as the ionizing photon production efficiency with
. We
find a relatively tight correlation between the [OIII]+H and UV
luminosity, which we use to derive for the first time the [OIII]+H
luminosity function (LF) at . The [OIII]+H LF is higher
at all luminosities compared to lower redshift, as opposed to the UV LF, due to
an increase of the [OIII]+H luminosity at a given UV luminosity from
to . Finally, using the [OIII]+H LF, we make
predictions for JWST/NIRSpec number counts of galaxies. We find that
the current wide-area extragalactic legacy fields are too shallow to use JWST
at maximal efficiency for spectroscopy even at 1hr depth and JWST
pre-imaging to mag will be required.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Photometric Constraints on the Redshift of z~10 candidate UDFj-39546284 from deeper WFC3/IR+ACS+IRAC observations over the HUDF
Ultra-deep WFC3/IR observations on the HUDF from the HUDF09 program revealed
just one plausible z~10 candidate UDFj-39546284. UDFj-39546284 had all the
properties expected of a galaxy at z~10 showing (1) no detection in the deep
ACS+WFC3 imaging data blueward of the F160W band, exhibiting (2) a blue
spectral slope redward of the break, and showing (3) no prominent detection in
deep IRAC observations. The new, similarly deep WFC3/IR HUDF12 F160W
observations over the HUDF09/XDF allow us to further assess this candidate.
These observations show that this candidate, previously only detected at ~5.9
sigma in a single band, clearly corresponds to a real source. It is detected at
~5.3 sigma in the new H-band data and at ~7.8 sigma in the full 85-orbit H-band
stack. Interestingly, the non-detection of the source (<1 sigma) in the new
F140W observations suggests a higher redshift. Formally, the best-fit redshift
of the source utilizing all the WFC3+ACS (and IRAC+K-band) observations is
11.8+/-0.3. However, we consider the z~12 interpretation somewhat unlikely,
since the source would either need to be ~20x more luminous than expected or
show very high-EW Ly-alpha emission (which seems improbable given the extensive
neutral gas prevalent early in the reionization epoch). Lower-redshift
solutions fail if only continuum models are allowed. Plausible lower-redshift
solutions require that the H-band flux be dominated by line emission such as
Halpha or [OIII] with extreme EWs. The tentative detection of line emission at
1.6 microns in UDFj-39546284 in a companion paper suggests that such emission
may have already been found.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters,
updated to match the version in pres
A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE
We present a spectroscopic redshift measurement of a very bright Lyman break
galaxy at z=7.7302+-0.0006 using Keck/MOSFIRE. The source was pre-selected
photometrically in the EGS field as a robust z~8 candidate with H=25.0 mag
based on optical non-detections and a very red Spitzer/IRAC [3.6]-[4.5]
broad-band color driven by high equivalent width [OIII]+Hbeta line emission.
The Lyalpha line is reliably detected at 6.1 sigma and shows an asymmetric
profile as expected for a galaxy embedded in a relatively neutral
inter-galactic medium near the Planck peak of cosmic reionization. The line has
a rest-frame equivalent width of EW0=21+-4 A and is extended with
V_FWHM=360+90-70 km/s. The source is perhaps the brightest and most massive z~8
Lyman break galaxy in the full CANDELS and BoRG/HIPPIES surveys, having
assembled already 10^(9.9+-0.2) M_sol of stars at only 650 Myr after the Big
Bang. The spectroscopic redshift measurement sets a new redshift record for
galaxies. This enables reliable constraints on the stellar mass, star-formation
rate, formation epoch, as well as combined [OIII]+Hbeta line equivalent widths.
The redshift confirms that the IRAC [4.5] photometry is very likely dominated
by line emission with EW0(OIII+Hbeta)= 720-150+180 A. This detection thus adds
to the evidence that extreme rest-frame optical emission lines are a ubiquitous
feature of early galaxies promising very efficient spectroscopic follow-up in
the future with infrared spectroscopy using JWST and, later, ELTs.Comment: 6 pages, 4 figures, small updates to match ApJL accepted versio
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Low-lying fermion modes, topology and light hadrons in quenched QCD
We explore the properties of low lying eigenmodes of fermions in the quenched
approximation of lattice QCD. The fermion action is a recently proposed overlap
action and has exact chiral symmetry. We find that chiral zero-eigenvalue modes
are localized in space and their positions correlate strongly with the
locations (as defined through the density of pure gauge observables) of
instantons of the appropriate charge. Nonchiral modes are also localized with
peaks which are strongly correlated with the positions of both charges of
instantons. These correlations slowly die away as the fermion eigenvalue rises.
Correlators made of quark propagators restricted to these modes closely
reproduce ordinary hadron correlators at small quark mass in many channels. Our
results are in qualitative agreement with the expectations of instanton liquid
models.Comment: 21 pages, Revtex, 21 postscript figures. COLO-HEP-45
Steady-state spin densities and currents
This article reviews steady-state spin densities and spin currents in
materials with strong spin-orbit interactions. These phenomena are intimately
related to spin precession due to spin-orbit coupling which has no equivalent
in the steady state of charge distributions. The focus will be initially on
effects originating from the band structure. In this case spin densities arise
in an electric field because a component of each spin is conserved during
precession. Spin currents arise because a component of each spin is continually
precessing. These two phenomena are due to independent contributions to the
steady-state density matrix, and scattering between the conserved and
precessing spin distributions has important consequences for spin dynamics and
spin-related effects in general. In the latter part of the article extrinsic
effects such as skew scattering and side jump will be discussed, and it will be
shown that these effects are also modified considerably by spin precession.
Theoretical and experimental progress in all areas will be reviewed
Anomalous Hall Effect and Skyrmion Number in Real- and Momentum-space
We study the anomalous Hall effect (AHE) for the double exchange model with
the exchange coupling being smaller than the bandwidth for the
purpose of clarifying the following unresolved and confusing issues: (i) the
effect of the underlying lattice structure, (ii) the relation between AHE and
the skyrmion number, (iii) the duality between real and momentum spaces, and
(iv) the role of the disorder scatterings; which is more essential,
(Hall conductivity) or (Hall resistivity)? Starting from a generic
expression for , we resolve all these issues and classify the regimes
in the parameter space of (: elastic-scattering time), and
(length scale of spin texture). There are two distinct mechanisms
of AHE; one is characterized by the real-space skyrmion-number, and the other
by momentum-space skyrmion-density at the Fermi level, which work in different
regimes of the parameter space.Comment: 4 pages, 1 figure, REVTe
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