5,747 research outputs found
Weak lensing mass reconstructions of the ESO Distant Cluster Survey
We present weak lensing mass reconstructions for the 20 high-redshift
clusters i n the ESO Distant Cluster Survey. The weak lensing analysis was
performed on deep, 3-color optical images taken with VLT/FORS2, using a
composite galaxy catalog with separate shape estimators measured in each
passband. We find that the EDisCS sample is composed primarily of clusters that
are less massive than t hose in current X-ray selected samples at similar
redshifts, but that all of the fields are likely to contain massive clusters
rather than superpositions of low mass groups. We find that 7 of the 20 fields
have additional massive structures which are not associated with the clusters
and which can affect the weak lensing mass determination. We compare the mass
measurements of the remaining 13 clusters with luminosity measurements from
cluster galaxies selected using photometric redshifts and find evidence of a
dependence of the cluster mass-to-light ratio with redshift. Finally we
determine the noise level in the shear measurements for the fields as a
function of exposure time and seeing and demonstrate that future ground-based
surveys which plan to perform deep optical imaging for use in weak lensing
measurements must achieve point-spread functions smaller than a median of 0.6"
FWHM.Comment: 35 pages, 24 figures, accepted to A&A, a version with better figure
resolution can be found at http://www.mpa-garching.mpg.de/ediscs/papers.htm
The Structure of the Cold Neutral ISM on 10-100 Astronomical Unit Scales
We have used the Very Long Baseline Array (VLBA) and the Very Large Array
(VLA) to image Galactic neutral hydrogen in absorption towards four compact
extragalactic radio sources with 10 milliarcsecond resolution. Previous VLBA
data by Faison et al (1998) have shown the existence of prominent structures in
the direction of the extragalactic source 3C~138 with scale sizes of 10-20 AU
with changes in HI optical depth in excess of 0.8 0.1. In this paper we
confirm the small scale \hi optical depth variations toward 3C~147 suggested
earlier at a level up to 20 % 5% . The sources 3C~119, 2352+495 and
0831+557 show no significant change in \hi optical depth across the sources
with one sigma limits of 30%, 50%, and 100%. Of the seven sources recently
investigated with the VLBA and VLA, only 3C~138 and 3C~147 show statistically
significant variations in HI opacities.
Deshpande (2000) have attempted to explain the observed small-scale structure
as an extension of the observed power spectrum of structure on parsec size
scales. The predictions of Deshpande (2000) are consistent with the VLBA HI
data observed in the directions of a number of sources, including 3C~147, but
are not consistent with our previous observations of the HI opacity structure
toward 3C~138
Wide field weak lensing observations of A1835 and A2204
We present mass reconstructions from weak lensing for the galaxy clusters
A1835 and A2204 over 34'x34' fields using data from the ESO/MPG Wide Field
Imager. Using a background galaxy population of 22<R<25.5 we detect the
gravitational shear of A1835 at 8.8 sigma significance, and obtain best-fit
mass profiles of sigma_v=1233^{+66}_{-70} km/s for a singular isothermal sphere
model and r_{200}=1550 h^{-1} kpc, c=2.96 for a `universal' CDM profile. Using
a color-selected background galaxy population of 22<R<25.8 we detect the
gravitational shear of A2204 at 7.2 sigma significance, and obtain best-fit
mass profiles of sigma_v=1035^{+65}_{-71} km/s for a SIS model and r_{200}=1310
h^{-1} km/s, c=6.3 for a `universal' CDM profile. The gravitational shear at
distances greater than 10' is significantly detected for both clusters. The
best fit weak lensing cluster masses agree well with both X-ray and dynamical
mass measurements, although the central concentration of A1835 is much lower in
the weak lensing mass profile than that measured by recent Chandra results. We
suggest that this lower concentration is most likely a combination of
contamination of the 'background' galaxy population with cluster dwarf galaxies
and the effect of a prolate or tri-axial cluster core with the major axis lying
near the plane of the sky. We also detect a number of additional structures at
moderate significance, some of which appear to be sub-haloes associated with
the clusters.Comment: accepted to A&A, 14 pages, 13 figures, version with higher quality
images can be found at http://www.uni-bonn.de/~clow
Diffuse retro-reflective imaging for improved mosquito tracking around human baited bednets
Robust imaging techniques for tracking insects have been essential tools in numerous laboratory and field studies on pests, beneficial insects and model systems. Recent innovations in optical imaging systems and associated signal processing have enabled detailed characterisation of nocturnal mosquito behaviour around bednets and improvements in bednet design, a global essential for protecting populations against malaria. Nonetheless, there remain challenges around ease of use for large scale in situ recordings and extracting data reliably in the critical areas of the bednet where the optical signal is attenuated. Here we introduce a retro-reflective screen at the back of the measurement volume, which can simultaneously provide diffuse illumination, and remove optical alignment issues whilst requiring only one-sided access to the measurement space. The illumination becomes significantly more uniform, although, noise removal algorithms are needed to reduce the effects of shot noise particularly across low intensity bednet regions. By systematically introducing mosquitoes in front and behind the bednet in lab experiments we are able to demonstrate robust tracking in these challenging areas. Overall, the retro-reflective imaging setup delivers mosquito segmentation rates in excess of 90% compared to less than 70% with back-lit systems
Parsec Scale Properties of Markarian 501
We present the results of a high angular resolution study of the BL Lac
object Markarian 501 in the radio band. We consider data taken at 14 different
epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new
Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We
study the kinematics of the parsec-scale jet and estimate its bulk velocity and
orientation with respect to the line of sight. Limb brightened structure in the
jet is clearly visible in our data and we discuss its possible origin in terms
of velocity gradients in the jet. Quasi-simultaneous multi-wavelength
observations allow us to map the spectral index distribution and to compare it
to the jet morphology. Finally, we estimate the physical parameters of the
parsec-scale jet.Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and
fig. 2 available only as .jpg files
PAHs in the Halo of NGC 5529
We present sensitive ISO m observations of the edge-on
galaxy, NGC 5529, finding an extensive MIR halo around NGC 5529. The emission
is dominated by PAHs in this band. The PAH halo has an exponential scale height
of 3.7 kpc but can still be detected as far as kpc from the plane
to the limits of the high dynamic range (1770/1) data. This is the most
extensive PAH halo yet detected in a normal galaxy. This halo shows
substructure and the PAHs likely originate from some type of disk outflow. PAHs
are long-lived in a halo environment and therefore continuous replenishment
from the disk is not required (unless halo PAHs are also being destroyed or
removed), consistent with the current low SFR of the galaxy. The PAHs correlate
spatially with halo H emission, previously observed by Miller &
Veilleux (2003); both components are likely excited/ionized by in-disk photons
that are leaking into the halo. The presence of halo gas may be related to the
environment of NGC 5529 which contains at least 17 galaxies in a small group of
which NGC 5529 is the dominant member. Of these, we have identified two new
companions from the SDSS.Comment: 16 pages, 5 gif figures, accepted for publication in A&A, For pdf
with higher quality figures, see http://www.astro.queensu.ca/~irwi
Accounting for the foreground contribution to the dust emission towards Kepler's supernova remnant
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15061.xWhether or not supernovae contribute significantly to the overall dust budget is a controversial subject. Submillimetre (sub-mm) observations, sensitive to cold dust, have shown an excess at 450 and 850 μm in young remnants Cassiopeia A (Cas A) and Kepler. Some of the sub-mm emission from Cas A has been shown to be contaminated by unrelated material along the line of sight. In this paper, we explore the emission from material towards Kepler using sub-mm continuum imaging and spectroscopic observations of atomic and molecular gas, via H i, 12CO(J= 2–1) and 13CO(J= 2–1). We detect weak CO emission (peak T*A = 0.2–1 K, 1–2 km s−1 full width at half-maximum) from diffuse, optically thin gas at the locations of some of the sub-mm clumps. The contribution to the sub-mm emission from foreground molecular and atomic clouds is negligible. The revised dust mass for Kepler's remnant is 0.1–1.2 M⊙ , about half of the quoted values in the original study by Morgan et al., but still sufficient to explain the origin of dust at high redshifts.Peer reviewe
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