653 research outputs found
The Serendipitous Discovery of a Group or Cluster of young Galaxies at z=2.40 in Deep Hubble Space Telescope WFPC2 Images
We report the serendipitous discovery of a group or cluster of young galaxies
at 2.40 in a 24-orbit HST/WFPC2 exposure of the field around the weak
radio galaxy 53W002. Potential cluster members were identified on ground-based
narrow-band redshifted Ly images and confirmed via spectroscopy.
In addition to the known weak radio galaxy 53W002 at z=2.390, two other
objects were found to have excess narrow-band Ly emission at
2.40. Both have been spectroscopically confirmed, and one clearly
contains a weak AGN. They are located within one arcminute of 53W002, or
Mpc (=0.5) at 2.40, which is the physical
scale of a group or small cluster of galaxies. Profile fitting of the WFPC2
images shows that the objects are very compact, with scale lengths
0\farcs 1 (kpc), and are rather faint
(luminosities < L*), implying that they may be sub-galactic sized objects. We
discuss these results in the context of galaxy and cluster evolution and the
role that weak AGN may play in the formation of young galaxies.Comment: Accepted for publication in The Astrophysical Journal (Letters). 13
pages of gzip compressed and uuencoded PS. Figures are available at
http://www.phys.unsw.edu.au/~spd/bib.htm
The Top Ten List of Gravitational Lens Candidates from the HST Medium Deep Survey
A total of 10 good candidates for gravitational lensing have been discovered
in the WFPC2 images from the HST Medium Deep Survey (MDS) and archival primary
observations. These candidate lenses are unique HST discoveries, i.e. they are
faint systems with sub-arcsecond separations between the lensing objects and
the lensed source images. Most of them are difficult objects for ground-based
spectroscopic confirmation or for measurement of the lens and source redshifts.
Seven are ``strong lens'' candidates which appear to have multiple images of
the source. Three are cases where the single image of the source galaxy has
been significantly distorted into an arc. The first two quadruply lensed
candidates were reported in Ratnatunga et al 1995 (ApJL, 453, L5) We report on
the subsequent eight candidates and describe them with simple models based on
the assumption of singular isothermal potentials. Residuals from the simple
models for some of the candidates indicate that a more complex model for the
potential will probably be required to explain the full structural detail of
the observations once they are confirmed to be lenses. We also discuss the
effective survey area which was searched for these candidate lens objects.Comment: 26 pages including 12 figures and 10 tables. AJ Vol. 117, No.
The technology potentials for satellite spacing and frequency sharing
Satellite spacing and frequency sharing in microwave relay system
New "Einstein Cross" Gravitational Lens Candidates in HST WFPC2 Survey Images
We report the serendipitous discovery of ``Einstein cross'' gravitational
lens candidates using the Hubble Space Telescope. We have so far discovered two
good examples of such lenses, each in the form of four faint blue images
located in a symmetric configuration around a red elliptical galaxy. The high
resolution of HST has facilitated the discovery of this optically selected
sample of faint lenses with small (~1 arcsec) separations between the (I ~
25-27) lensed components and the much brighter (I ~ 19-22) lensing galaxies.
The sample has been discovered in the routine processing of HST fields through
the Medium Deep Survey pipeline, which fits simple galaxy models to broad band
filter images of all objects detected in random survey fields using WFPC2.
We show that the lens configuration can be modeled using the gravitational
field potential of a singular isothermal ellipsoidal mass distribution. With
this model the lensing potential is very similar, both in ellipticity and
orientation, to the observed light distribution of the elliptical galaxy, as
would occur when stars are a tracer population. The model parameters and
associated errors have been derived by 2-dimensional analysis of the observed
images. The maximum likelihood procedure iteratively converges simultaneously
on the model for the lensing elliptical galaxy and the source of the lensed
components. A systematic search is in progress for other gravitational lens
candidates in the HST Medium Deep Survey. This should eventually lead to a good
statistical estimate for lensing probabilities, and enable us to probe the
cosmological component of the observed faint blue galaxy population.Comment: Accepted for Astrophysical Journal Letters, 1995 November 1 LaTex, 10
pages, includes 2 figures 1 table, tarred gzip uuencoded using uufiles scrip
Sigma1 Targeting to Suppress Aberrant Androgen Receptor Signaling in Prostate Cancer.
Suppression of androgen receptor (AR) activity in prostate cancer by androgen depletion or direct AR antagonist treatment, although initially effective, leads to incurable castration-resistant prostate cancer (CRPC) via compensatory mechanisms including resurgence of AR and AR splice variant (ARV) signaling. Emerging evidence suggests that Sigma1 (also known as sigma-1 receptor) is a unique chaperone or scaffolding protein that contributes to cellular protein homeostasis. We reported previously that some Sigma1-selective small molecules can be used to pharmacologically modulate protein homeostasis pathways. We hypothesized that these Sigma1-mediated responses could be exploited to suppress AR protein levels and activity. Here we demonstrate that treatment with a small-molecule Sigma1 inhibitor prevented 5α- dihydrotestosterone-mediated nuclear translocation of AR and induced proteasomal degradation of AR and ARV, suppressing the transcriptional activity and protein levels of both full-length and splice-variant AR. Consistent with these data, RNAi knockdown of Sigma1 resulted in decreased AR levels and transcriptional activity. Furthermore, Sigma1 physically associated with ARV7 and A
Canine Morphology: Hunting for Genes and Tracking Mutations
In this essay, Abigail Shearin and Elaine Ostrander discuss the proposed genomic mechanisms for the extraordinary level of phenotypic variation observed in the domestic dog and the evidence detailing the variants responsible for the many shapes, sizes, textures, and colors of man's best friend
The morphological mix of field galaxies to I=24.25 magnitudes (b=26 magnitudes) from a deep Hubble Space Telescope WFPC2 image
We determine the morphological mix of field galaxies down to mag ( mag) from a single ultradeep HST WFPC2 image in
both the and filters. In total, we find 227 objects with
mag and classify these into three types: ellipticals (16%),
early-type spirals (37%) and late-type spirals/Irregulars (47%). The
differential number counts for each type are compared to simple models in a
standard flat cosmology. We find that both the elliptical and early-type spiral
number counts are well described by {\it little or no}-evolution models, but
only when normalized at mag. Given the uncertainties in the
luminosity function (LF) normalization, both populations are consistent with a
mild evolutionary scenario based on a normal/low rate of star-formation. This
constrains the end of the last {\it major} star-formation epoch in the giant
galaxy populations to .
Conversely, the density of the observed late-type/Irregular population is
found to be a factor of 10 in excess of the conventional no-evolution model.
This large population might be explained by either a modified {\it local}
dwarf-rich LF, and/or strong evolution acting on the {\it local} LF. For the
dwarf-rich case, a {\it steep} faint-end Schechter-slope ()
is required plus a five-fold increase in the dwarf normalization. For a purely
evolving model based on a {\it flat} Loveday {\it et al.} (1992) LF
(), a ubiquitous starburst of 2.0 mag is
needed at z for the {\it entire} late-type population. We argue for
a combination of these possibilities, and show that for a steep Marzke {\it et
al.} (1994) LF (), a starburst of 1.3 mag is requiredComment: 9 pages, 3 figures (2 colour). The figures are available at
http://www.phys.unsw.edu.au/~spd/bib.htm
Fine mapping a locus controlling leg morphology in the domestic dog
The domestic dog offers a remarkable opportunity to disentangle the genetics of complex phenotypes. Here, we explore a locus, previously identified in the Portuguese water dog (PWD), associated with PC2, a morphological principal component characterized as leg width versus leg length. The locus was initially mapped to a region of 26 Mb on canine chromosome 12 (CFA12) following a genome-wide scan. Subsequent and extensive genotyping of single-nucleotide polymorphisms (SNPs) and haplotype analysis in both the PWD and selected breeds representing phenotypic extremes of PC2 reduced the region from 26 Mb to 500 kb. The proximity of the critical interval to two collagen genes suggests that the phenotype may be controlled by cis-acting mechanisms
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