573 research outputs found
Searching for z ~ 6 Objects with the HST Advanced Camera for Surveys: Preliminary Analysis of a Deep Parallel Field
Recent results suggest that z ~ 6 marks the end of the reionization era. A
large sample of objects at z ~ 6, therefore, will be of enormous importance, as
it will enable us to observationally determine the exact epoch of the
reionization and the sources that are responsible for it. With the HST Advanced
Camera for Surveys (ACS) coming on line, we now have an unique opportunity to
discover a significant number of objects at z ~ 6. The pure parallel mode
implemented for the Wide Field Camera (WFC) has greatly enhanced this ability.
We present our preliminary analysis of a deep ACS/WFC parallel field at
|b|=74.4^o. We find 30 plausible z ~ 6 candidates, all of which have S/N > 7 in
the F850LP-band. The major source of contamination could be faint Galactic cool
dwarfs, and we estimated that they would contribute at most 4 objects to our
candidate list. We derived the cumulative number density of galaxies at 6.0 <=
z <= 6.5 as 2.3 arcmin^{-2} to a limit of 28.0 mag in the F850LP-band, which is
slightly higher than our prediction. If this is not due to an underestimated
contamination rate, it could possibly imply that the faint-end slope of the z ~
6 luminosity function is steeper than alpha=-1.6. At the very least, our result
suggests that galaxies with L<L^* do exist in significant number at z ~ 6 and
they could be the major sources that contributed to the reionizing photons.Comment: accepted for publication in the ApJL; replaced with slightly modified
versio
Endoscopic Retrograde Cholangiopancreatography Treatment of Cholecystitis: Possible? Yes; Practical??
Classically, until now, the management of cholecystitis has consisted of immediate and judicious
clinical assessment of the affected patient, interpolating into the assessment of the physical findings
and results from appropriate laboratory, x-ray, and scanning techniques (sonography and scintigraphy)
to formulate a clinical impression. Usually, after the diagnosis has been established, the patient
is subjected to a cholecystectomy, although the timing of the surgery may vary depending on the
clinical condition of the patient. Alternatives to this management (cholecystectomy, medical management)
scheme have been suggested, but these are dependent upon the clinical condition ofthe patient
and considerations of risks. Percutaneous drainage of the gallbladder or cholecystostomy is
sufficient enough to provide drainage, relieve obstruction, and the consequences of infection, i.e.,
sepsis, and prevent perforation. A contributory role of endoscopic retrograde cholangiopancreatography
(ERCP) in this schema has not been a consideration. An ERCP is rarely employed for therapy
(or diagnosis) when cholecystitis is suspected but it might assume a more significant role if it is considered
an efficacious alternative in specific conditions. We have had the unusual experience of managing
11 patients with cholecystitis employing ERCP and its therapeutic modalities, i.e.,
sphincterotomy, selective cannulation of the cystic duct, and relieving obstruction of that structure
by catheter displacement of an obstructing stone. Endoscopic techniques providing decompression
of the gallbladder are described, and the feasibility of utilizing endoscopic procedures for treatment
of cholecystitis will be given consideration
Stent Scraping for Histology: An Alternative Method for Obtaining Tissue to Rule out Neoplasia
Despite improvement in diagnostic modalities, confirmation of a histologic diagnosis of cancer of
the biliary tree and pancreas remains elusive. Attempts to collect positive cytology specimens from
vigorous brushings or washings obtained at endoscopy or percutaneously are often unsuccessful. In
our unit, we have increased the yield by obtaining tissue scraped from prostheses that have been previously
placed in either the bile duct or the pancreatic duct. The stents are first flushed with saline
to collect cytology specimens, after which, they are bisected and scraped, and these contents are prepared
in a manner similar to that used to prepare biopsy samples. Twelve of 16 scraped samples, 9
bile duct and 3 pancreas, were positive for adenocarcinoma. The cytology specimens were positive
in only 4 of the 12. We recommend this method of sampling from material contained within prostheses
as an adjunct when previous brushings, washings, or biopsies are negative
How JWST can measure First Light, Reionization and Galaxy Assembly
We summarize the design and performance of the James Webb Space Telescope
that is to be launched to an L2 orbit in 2011, and how it is designed, in
particular, to study the epochs of First Light, Reionization and Galaxy
Assembly.Comment: 12 pages, Latex2e requires 'elsart' (included), 7 Postscript figures.
To appear in the Proceedings of the UC Irvine Workshop on "First Light and
Reionization: Theoretical Study and Experimental Detection of the First
Luminous Sources", eds. A. Cooray & E. Barton (New Astron. Rev., 2005). A
full-resolution PDF version is available at www.asu.edu/clas/hst/www/jwst/ .
Revision includes minor corrections and legible labels in Fig.
Luminous Lyman-alpha Emitters with Very Blue UV-continuum Slopes at Redshift 5.7 <= z <= 6.6
We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame
UV continua at . These LAEs have previous HST and Spitzer
IRAC observations. Combining our newly acquired HST images, we find that their
UV-continuum slopes are in a range of . Unlike
previous, tentative detections of in photometrically
selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and
luminous ( mag). We model their broadband spectral energy
distributions (SEDs), and find that two galaxies can be
well fitted with young and dust-free stellar populations. However, it becomes
increasingly difficult to fit bluer galaxies. We explore further
interpretations by including non-zero LyC escape fraction , very
low metallicities, and/or AGN contributions. Assuming ,
we achieve the bluest slopes when nebular emission is
considered. This can nearly explain the SEDs of two galaxies with
and --2.9 (). Larger
values and very low metallicities are not favored by the strong nebular line
emission (evidenced by the IRAC flux) or the observed (IRAC 1 - IRAC 2) color.
Finally, we find that the galaxy can potentially be well
explained by the combination of a very young population with a high () and an old, dusty population. We are not able to produce two
galaxies. Future deep spectroscopic observations are
needed to fully understand these galaxies.Comment: Published in ApJ on 2020 Feb 1; Authors' version (9 pages); See
published version at
https://iopscience.iop.org/article/10.3847/1538-4357/ab64e
A Simple Prediction on the Surface Density of Galaxies at z ~ 6
Systematic surveys are being proposed to discover a significant number of
galaxies at z ~ 6, which is now suggested as the epoch when the reionization
era of the Universe ends. To plan such surveys, we need a reasonable
expectation of the surface density of high redshift galaxies at different flux
limits. Here we present a simple prediction of the surface density of 5.5 < z <
6.5 galaxies in the optical regime, extrapolating from what is already known
about galaxies at z ~ 3. This prediction is consistent with the results of
nearly all known searches for objects at z ~ 6, giving confidence that we may
use it to plan optimal combination of survey depth and sky coverage in
searching for such objects. We suggest that the most efficient strategy with
existing ground-based facilities is to do medium-depth (m_{AB}= 24.0 -- 24.5
mag), wide-field (a couple of square degrees) survey using a wide-field camera
at a 4m-class telescope. As the predicted surface density at this brightness
level is very sensitive to the value of L*, the result of such a survey can be
easily used to constrain the luminosity evolution from z ~ 3 to 6.Comment: Accepted for publication in the Astrophysical Journa
Ultra-deep Large Binocular Camera U-band Imaging of the GOODS-North Field: Depth vs. Resolution
We present a study of the trade-off between depth and resolution using a
large number of U-band imaging observations in the GOODS-North field
(Giavalisco et al. 2004) from the Large Binocular Camera (LBC) on the Large
Binocular Telescope (LBT). Having acquired over 30 hours of data (315 images
with 5-6 mins exposures), we generated multiple image mosaics, starting with
the best atmospheric seeing images (FWHM 0.8"), which constitute
10% of the total data set. For subsequent mosaics, we added in data with
larger seeing values until the final, deepest mosaic included all images with
FWHM 1.8" (94% of the total data set). From the mosaics, we
made object catalogs to compare the optimal-resolution, yet shallower image to
the lower-resolution but deeper image. We show that the number counts for both
images are 90% complete to . Fainter than
27, the object counts from the optimal-resolution image start to
drop-off dramatically (90% between = 27 and 28 mag), while the deepest
image with better surface-brightness sensitivity ( 32
mag arcsec) show a more gradual drop (10% between 27
and 28 mag). For the brightest galaxies within the GOODS-N field, structure and
clumpy features within the galaxies are more prominent in the
optimal-resolution image compared to the deeper mosaics. Finally, we find - for
220 brighter galaxies with 24 mag - only marginal
differences in total flux between the optimal-resolution and lower-resolution
light-profiles to 32 mag arcsec. In only 10% of
the cases are the total-flux differences larger than 0.5 mag. This helps
constrain how much flux can be missed from galaxy outskirts, which is important
for studies of the Extragalactic Background Light.Comment: 24 pages, 14 figures, submitted to PASP, comments welcom
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