21 research outputs found
Efficient least-squares basket-weaving
We report on a novel method to solve the basket-weaving problem.
Basket-weaving is a technique that is used to remove scan-line patterns from
single-dish radio maps. The new approach applies linear least-squares and works
on gridded maps from arbitrarily sampled data, which greatly improves
computational efficiency and robustness. It also allows masking of bad data,
which is useful for cases where radio frequency interference is present in the
data. We evaluate the algorithms using simulations and real data obtained with
the Effelsberg 100-m telescope.Comment: 11 pages, 11 figures, accepted by A&
Using negative detections to estimate source finder reliability
We describe a simple method to determine the reliability of source finders
based on the detection of sources with both positive and negative total flux.
Under the assumption that the noise is symmetric and that real sources have
positive total flux, negative detections can be used to assign to each positive
detection a probability of being real. We discuss this method in the context of
upcoming, interferometric HI surveys.Comment: Accepted for publication on the 2012 PASA source finding special
issu
The Effelsberg-Bonn HI Survey: Data reduction
Starting in winter 2008/2009 an L-band 7-Feed-Array receiver is used for a
21-cm line survey performed with the 100-m telescope, the Effelsberg-Bonn HI
survey (EBHIS). The EBHIS will cover the whole northern hemisphere for decl.>-5
deg comprising both the galactic and extragalactic sky out to a distance of
about 230 Mpc. Using state-of-the-art FPGA-based digital fast Fourier transform
spectrometers, superior in dynamic range and temporal resolution to
conventional correlators, allows us to apply sophisticated radio frequency
interference (RFI) mitigation schemes.
In this paper, the EBHIS data reduction package and first results are
presented. The reduction software consists of RFI detection schemes, flux and
gain-curve calibration, stray-radiation removal, baseline fitting, and finally
the gridding to produce data cubes. The whole software chain is successfully
tested using multi-feed data toward many smaller test fields (1--100 square
degrees) and recently applied for the first time to data of two large sky
areas, each covering about 2000 square degrees. The first large area is toward
the northern galactic pole and the second one toward the northern tip of the
Magellanic Leading Arm. Here, we demonstrate the data quality of EBHIS Milky
Way data and give a first impression on the first data release in 2011.Comment: 17 pages, 14 figures; to be published in ApJ
2D-1D Wavelet Reconstruction As A Tool For Source Finding In Spectroscopic Imaging Surveys
Today, image denoising by thresholding of wavelet coefficients is a commonly
used tool for 2D image enhancement. Since the data product of spectroscopic
imaging surveys has two spatial and one spectral dimension, the techniques for
denoising have to be adapted to this change in dimensionality. In this paper we
will review the basic method of denoising data by thresholding wavelet
coefficients and implement a 2D-1D wavelet decomposition to obtain an efficient
way of denoising spectroscopic data cubes. We conduct different simulations to
evaluate the usefulness of the algorithm as part of a source finding pipeline.Comment: 8 pages, 7 figures, 1 table, accepted for publication in PASA Special
Issue on Source Finding and Visualizatio
The high-velocity cloud complex Galactic Center Negative as seen by EBHIS and GASS. I. Cloud catalog and global properties
Using Milky Way data of the new Effelsberg-Bonn HI Survey (EBHIS) and the
Galactic All-Sky Survey (GASS), we present a revised picture of the
high-velocity cloud (HVC) complex Galactic Center Negative (GCN). Owing to the
higher angular resolution of these surveys compared to previous studies (e.g.,
the Leiden Dwingeloo Survey), we resolve Complex GCN into lots of individual
tiny clumps, that mostly have relatively broad line widths of more than 15
km/s. We do not detect a diffuse extended counterpart, which is unusual for an
HVC complex. In total 243 clumps were identified and parameterized which allows
us to statistically analyze the data. Cold-line components (i.e., w < 7.5 km/s)
are found in about 5% only of the identified cloudlets. Our analysis reveals
that Complex GCN is likely built up of several subpopulations that do not share
a common origin. Furthermore, Complex GCN might be a prime example for warm-gas
accretion onto the Milky Way, where neutral HI clouds are not stable against
interaction with the Milky Way gas halo and become ionized prior to accretion.Comment: 13 pages, 19 figures; accepted by A&
Dust in a compact, cold, high-velocity cloud: A new approach to removing foreground emission
Context. Because isolated high-velocity clouds (HVCs) are found at great distances from the Galactic radiation field and because they have subsolar metallicities, there have been no detections of dust in these structures. A key problem in this search is the removal of foreground dust emission.
Aims. Using the Effelsberg-Bonn H 
EZOA - a catalogue of EBHIS H I-detected galaxies in the northern Zone of Avoidance
We present a catalogue of galaxies in the northern Zone of Avoidance (ZoA),
extracted from the shallow version of the blind HI survey with the Effelsberg
100 m radio telescope, EBHIS, that has a sensitivity of 23 mJy/beam at 10.24
km/s velocity resolution. The catalogue comprises 170 detections in the region
Dec >= -5 degrees and |b| < 6 degrees. About a third of the detections (N=67)
have not been previously recorded in HI. While 29 detections have no
discernible counterpart at any wavelength other than HI, 48 detections (28%)
have a counterpart visible on optical or NIR images but are not recorded as
such in the literature. New HI detections were found as close as 7.5 Mpc (EZOA
J2120+45), and at the edge of the Local Volume, at 10.1 Mpc, we have found two
previously unknown dwarf galaxies (EZOA J0506+31 and EZOA J0301+56). Existing
large-scale structures crossing the northern ZoA have been established more
firmly by the new detections, with the possibility of new filaments. We
conclude that the high rate of 39% new HI\detections in the northern ZoA, which
has been extensively surveyed with targeted observations in the past, proves
the power of blind HI surveys. The full EBHIS survey, which will cover the full
northern sky with a sensitivity comparable to the HIPASS survey of the southern
sky, is expected to add many new detections and uncover new structures in the
northern ZoA.Comment: 19 pages, 10 figures, accepted by MNRAS, online material available
through MNRAS or by reques
Contribution a la formalisation du concept de flexibilite des systemes industriels. Etudes de cas pratiques
SIGLEINIST T 74961 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc