1,243 research outputs found
Simultaneous Multicolor Detection of Faint Galaxies in the Hubble Deep Field
We present a novel way to detect objects when multiband images are available.
Typically, object detection is performed in one of the available bands or on a
somewhat arbitrarily co-added image. Our technique provides an almost optimal
way to use all the color information available. We build up a composite image
of the N passbands where each pixel value corresponds to the probability that
the given pixel is just sky. By knowing the probability distribution of sky
pixels (a chi-square distribution with N degrees of freedom), the data can be
used to derive the distribution of pixels dominated by object flux. From the
two distributions an optimal segmentation threshold can be determined. Clipping
the probability image at this threshold yields a mask, where pixels unlikely to
be sky are tagged. After using a standard connected-pixel criterion, the
regions of this mask define the detected objects. Applying this technique to
the Hubble Deep Field data, we find that we can extend the detection limit of
the data below that possible using linearly co-added images. We also discuss
possible ways of enhancing object detection probabilities for certain well
defined classes of objects by using various optimized linear combinations of
the pixel fluxes (optimal subspace filtering).Comment: 8 pages, 5 figures (4 postscript, 1 JPEG). To be published in A
The Dark Matter Contribution to Galactic Diffuse Gamma Ray Emission
Observations of diffuse Galactic gamma ray emission (DGE) by the Fermi Large
Area Telescope (LAT) allow a detailed study of cosmic rays and the interstellar
medium. However, diffuse emission models of the inner Galaxy underpredict the
Fermi-LAT data at energies above a few GeV and hint at possible
non-astrophysical sources including dark matter (DM) annihilations or decays.
We present a study of the possible emission components from DM using the
high-resolution Via Lactea II N-body simulation of a Milky Way-sized DM halo.
We generate full-sky maps of DM annihilation and decay signals that include
modeling of the adiabatic contraction of the host density profile, Sommerfeld
enhanced DM annihilations, -wave annihilations, and decaying DM. We compare
our results with the DGE models produced by the Fermi-LAT team over different
sky regions, including the Galactic center, high Galactic latitudes, and the
Galactic anti-center. This work provides possible templates to fit the
observational data that includes the contribution of the subhalo population to
DM gamma-ray emission, with the significance depending on the
annihilation/decay channels and the Galactic regions being considered.Comment: Published by PR
All degree six local unitary invariants of k qudits
We give explicit index-free formulae for all the degree six (and also degree
four and two) algebraically independent local unitary invariant polynomials for
finite dimensional k-partite pure and mixed quantum states. We carry out this
by the use of graph-technical methods, which provides illustrations for this
abstract topic.Comment: 18 pages, 6 figures, extended version. Comments are welcom
Apparent Clustering of Intermediate-redshift Galaxies as a Probe of Dark Energy
We show the apparent redshift-space clustering of galaxies in redshift range
of 0.2--0.4 provides surprisingly useful constraints on dark energy component
in the universe, because of the right balance between the density of objects
and the survey depth. We apply Fisher matrix analysis to the the Luminous Red
Galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS), as a concrete example.
Possible degeneracies in the evolution of the equation of state (EOS) and the
other cosmological parameters are clarified.Comment: 5 pages, 3 figures, Phys.Rev.Lett., replaced with the accepted
versio
High efficacy of photodynamic therapy on rat endometrium after systemic administration of benzoporphyrin derivative monoacid ring A
BACKGROUND: The aim of this study was to evaluate the effect of the benzoporphyrin derivative monoacid ring A (verteporfin)âmediated photodynamic therapy (PDT) on rat endometrium and to determine the optimal drug concentration for endometrial ablation. METHODS: Five minutes after i.v. injection of different concentrations of verteporfin into 24 female Sprague-Dawley rats, 630nm light treatment was delivered for 500 s (120J/cm2) to the left horn of the uterus. The 24 rats were divided into six groups according to the drug dose injected, four rats per group: group I (2 mg/kg), group II (1 mg/kg), and groups III, IV, V and VI with 0.5, 0.25, 0.125 and 0.0625mg/kg respectively. Four days later, the rat uteri were analysed by light microscopy. RESULTS: Endometrial destruction was seen in all six groups, with the most significant result in group I (P < 0.008). Conservation of the myometrium was most significant in groups III, IV, V and VI. Acute inflammatory cells in the stromal endometrium were recorded mainly in groups I and II. However, the drug dosage that was most significant in destroying the glands with conservation of the myometrium and not causing severe inflammation was between 0.5 and 0.125mg/kg. CONCLUSIONS: Verteporfin was effective in endometrial ablation in all our animal groups, and the dose range of 0.5-0.125mg/kg appeared to be adequate. This observation will have to be scaled for clinical applicatio
Large Scale Clustering of Sloan Digital Sky Survey Quasars: Impact of the Baryon Density and the Cosmological Constant
We report the first result of the clustering analysis of Sloan Digital Sky
Survey (SDSS) quasars. We compute the two-point correlation function (2PCF) of
SDSS quasars in redshift space at ,
with particular attention to its baryonic signature. Our sample consists of
19986 quasars extracted from the SDSS Data Release 4 (DR4). The redshift range
of the sample is (the mean redshift is )
and the reddening-corrected -band apparent magnitude range is . Due to the relatively low number density of the
quasar sample, the bump in the power spectrum due to the baryon density,
, is not clearly visible. The effect of the baryon density is,
however, to distort the overall shape of the 2PCF.The degree of distortion
makes it an interesting alternate measure of the baryonic signature. Assuming a
scale-independent linear bias and the spatially flat universe, i.e.,
, where
and denote the density parameters of dark matter and the
cosmological constant, we combine the observed quasar 2PCF and the predicted
matter 2PCF to put constraints on and . Our
result is fitted as at the 2 confidence level, which is consistent with
results from other cosmological observations such as WMAP. (abridged)Comment: 26 pages, 12 figures, Accepted for publication in the PAS
Caltech Faint Galaxy Redshift Survey X: A Redshift Survey in the Region of the Hubble Deep Field North
A redshift survey has been carried out in the region of the Hubble Deep Field
North using the Low Resolution Imaging Spectrograph at the Keck Observatory.
The resulting redshift catalog, which contains 671 entries, is a compendium of
our own data together with published LRIS/Keck data. It is more than 92%
complete for objects, irrespective of morphology, to mag in the HDF
itself and to mag in the Flanking Fields within a diameter of 8 arcmin
centered on the HDF, an unusually high completion for a magnitude limited
survey performed with a large telescope. A median redshift is reached
at .
Strong peaks in the redshift distribution, which arise when a group or poor
cluster of galaxies intersect the area surveyed, can be identified to in this dataset. More than 68% of the galaxies are members of these
redshift peaks. In a few cases, closely spaced peaks in can be resolved
into separate groups of galaxies that can be distinguished in both velocity and
location on the sky.
The radial separation of these peaks in the pencil-beam survey is consistent
with a characteristic length scale for the their separation of 70 Mpc
in our adopted cosmology (, ). Strong
galaxy clustering is in evidence at all epochs back to . (abstract
abridged)Comment: Accepted to the ApJ. This version contains all the figures and
tables. 2 minor typos in table 2b correcte
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