912 research outputs found
PMN J1632-0033: A new gravitationally lensed quasar
We report the discovery of a gravitationally lensed quasar resulting from our
survey for lenses in the southern sky. Radio images of PMN J1632-0033 with the
VLA and ATCA exhibit two compact, flat-spectrum components with separation
1.47" and flux density ratio 13.2. Images with the HST reveal the optical
counterparts to the radio components and also the lens galaxy. An optical
spectrum of the bright component, obtained with the first Magellan telescope,
reveals quasar emission lines at redshift 3.42. Deeper radio images with MERLIN
and the VLBA reveal a faint third radio component located near the center of
the lens galaxy, which is either a third image of the background quasar or
faint emission from the lens galaxy.Comment: 21 pp., including 4 figures; thoroughly revised in light of new
MERLIN/HST data; accepted for publication in A
A nearly symmetric double-image gravitational lens
We report the discovery of a new double-image gravitational lens resulting
from our search for lenses in the southern sky. Radio source PMN J2004-1349 is
composed of two compact components separated by 1.13 arcseconds in VLA, MERLIN
and VLBA images. The components have a flux ratio of 1:1 at radio frequencies
ranging from 5 GHz to 22 GHz. The I-band optical counterpart is also an equal
double, with roughly the same separation and position angle as the radio
double. Upon subtraction of the components from the I-band image, we identify a
dim pattern of residuals as the lens galaxy. While the present observations are
sufficient to establish that J2004-1349 is a gravitational lens, additional
information will be necessary (such as the redshifts of the galaxy and quasar,
and precise astrometry and photometry of the lens galaxy) before constructing
detailed mass models.Comment: 17 pp., 5 bitmapped figs. (contact [email protected] for nicer figs), in
press, A.J. (substantially revised
PMN J1838-3427: A new gravitationally lensed quasar
We report the discovery of a new double-image quasar that was found during a
search for gravitational lenses in the southern sky. Radio source PMN
J1838-3427 is composed of two flat-spectrum components with separation 1", flux
density ratio 14:1 and matching spectral indices, in VLA and VLBA images.
Ground-based BRI images show the optical counterpart (total I=18.6) is also
double with the same separation and position angle as the radio components. An
HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27:1) is
higher than the radio value probably due to differential extinction of the
components by the lens galaxy. An optical spectrum of the bright component
contains quasar emission lines at z=2.78 and several absorption features,
including prominent Ly-alpha absorption. The lens galaxy redshift could not be
measured but is estimated to be z=0.36 +/- 0.08. The image configuration is
consistent with the simplest plausible models for the lens potential. The flat
radio spectrum and observed variability of PMN J1838-3427 suggest the time
delay between flux variations of the components is measurable, and could thus
provide an independent measurement of H_0.Comment: 23 pages, incl. 6 figures, to appear in A.J.; replaced with accepted
version; minor changes to text, improved figure
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Investigation of Founder Effects for the Thr377Met Myocilin Mutation in Glaucoma Families from Differing Ethnic Backgrounds
Purpose: The aim of this study was to determine if there is a common founder for the Thr377Met myocilin mutation in primary open angle glaucoma (POAG) families with various ethnic backgrounds. Methods: Genomic DNA of 24 POAG-affected individuals from nine pedigrees with the Thr377Met mutation and 104 unaffected family members was genotyped with six microsatellite markers and four single nucleotide polymorphisms. The families were from Greece, India, Finland, the USA, and Australia. To assess the degree of linkage disequilibrium across MYOC in the general population we also investigated data generated from the HapMap consortium. Results: Three distinct haplotypes associated with the Thr377Met myocilin mutation were identified. The families from the USA and Greece, as well as the three Australian families originating from Greece and the former Yugoslavian Republic of Macedonia had one common haplotype. Interestingly, however, HapMap data suggest that linkage disequilibrium across MYOC was not strong. Conclusions: The Thr377Met myocilin mutation has arisen at least three separate times. Evidence for genetic founder effects in this prevalent age-related, yet heterogeneous, disease has important implications for future gene identification strategies
Hydrogen Epoch of Reionization Array (HERA)
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to
measure 21 cm emission from the primordial intergalactic medium (IGM)
throughout cosmic reionization (), and to explore earlier epochs of our
Cosmic Dawn (). During these epochs, early stars and black holes
heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is
designed to characterize the evolution of the 21 cm power spectrum to constrain
the timing and morphology of reionization, the properties of the first
galaxies, the evolution of large-scale structure, and the early sources of
heating. The full HERA instrument will be a 350-element interferometer in South
Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz.
Currently, 19 dishes have been deployed on site and the next 18 are under
construction. HERA has been designated as an SKA Precursor instrument.
In this paper, we summarize HERA's scientific context and provide forecasts
for its key science results. After reviewing the current state of the art in
foreground mitigation, we use the delay-spectrum technique to motivate
high-level performance requirements for the HERA instrument. Next, we present
the HERA instrument design, along with the subsystem specifications that ensure
that HERA meets its performance requirements. Finally, we summarize the
schedule and status of the project. We conclude by suggesting that, given the
realities of foreground contamination, current-generation 21 cm instruments are
approaching their sensitivity limits. HERA is designed to bring both the
sensitivity and the precision to deliver its primary science on the basis of
proven foreground filtering techniques, while developing new subtraction
techniques to unlock new capabilities. The result will be a major step toward
realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table
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