1,145 research outputs found
Observing the CMB with the AMiBA
I discuss the capabilities and limitations of the AMiBA for imaging CMB
anisotropies. Michael Kesteven (ATNF-CSIRO) has proposed drift-scanning as an
observing strategy for measuring and rejecting any instrumental response that
the close-packed interferometers may have to the local environment. The
advantages of mosaic imaging CMB anisotropies using a co-mounted
interferometric array in a drift-scanning observing mode are discussed. A
particular case of mosaic imaging a sky strip using a two-element AMiBA
prototype interferometer is considered and the signal-to-noise ratio in the
measurement of sky anisotropy using this observing strategy is analysed.Comment: 6 pages, includes 2 figures, to appear in the ASP Conf Ser.
proceedings of AMiBA 2001: High-z clusters, Missing baryons, and CMB
polarizatio
A Complete Sample of Megaparsec Size Double Radio Sources from SUMSS
We present a complete sample of megaparsec-size double radio sources compiled
from the Sydney University Molonglo Sky Survey (SUMSS). Almost complete
redshift information has been obtained for the sample. The sample has the
following defining criteria: Galactic latitude |b| > 12.5 deg, declination <
-50 deg and angular size > 5 arcmin. All the sources have projected linear size
larger than 0.7 Mpc (assuming H_o = 71 km/s/Mpc). The sample is chosen from a
region of the sky covering 2100 square degrees. In this paper, we present
843-MHz radio images of the extended radio morphologies made using the Molonglo
Observatory Synthesis Telescope (MOST), higher resolution radio observations of
any compact radio structures using the Australia Telescope Compact Array
(ATCA), and low resolution optical spectra of the host galaxies from the 2.3-m
Australian National University (ANU) telescope at Siding Spring Observatory.
The sample presented here is the first in the southern hemisphere and
significantly enhances the database of known giant radio sources. The giant
radio sources with linear size exceeding 0.7 Mpc have an abundance of (215
Mpc)^(-3) at the sensitivity of the survey. In the low redshift universe, the
survey may be suggesting the possibility that giant radio sources with relict
lobes are more numerous than giant sources in which beams from the centre
currently energize the lobes.Comment: 67 pages, 29 figures, for full resolution figures see
http://www.astrop.physics.usyd.edu.au/SUMSS/PAPERS/Submit-May11-ms.pd
ATLBS Extended Source Sample: The evolution in radio source morphology with flux density
Based on the ATLBS survey we present a sample of extended radio sources and
derive morphological properties of faint radio sources. 119 radio galaxies form
the ATLBS-Extended Source Sample (ATLBS-ESS) consisting of all sources
exceeding 30" in extent and integrated flux densities exceeding 1 mJy. We give
structural details along with information on galaxy identifications and source
classifications. The ATLBS-ESS, unlike samples with higher flux-density limits,
has almost equal fractions of FR-I and FR-II radio galaxies with a large
fraction of the FR-I population exhibiting 3C31-type structures. Significant
asymmetry in lobe extents appears to be a common occurrence in the ATLBS-ESS
FR-I sources compared to FR-II sources. We present a sample of 22 FR-Is at
z>0.5 with good structural information. The detection of several giant radio
sources, with size exceeding 0.7 Mpc, at z>1 suggests that giant radio sources
are not less common at high redshifts. The ESS also includes a sample of 28
restarted radio galaxies. The relative abundance of dying and restarting
sources is indicative of a model where radio sources undergo episodic activity
in which an active phase is followed by a brief dying phase that terminates
with restarting of the central activity; in any massive elliptical a few such
activity cycles wherein adjacent events blend may constitute the lifetime of a
radio source and such bursts of blended activity cycles may be repeated over
the age of the host. The ATLBS-ESS includes a 2-Mpc giant radio galaxy with the
lowest surface brightness lobes known to date.Comment: 69 pages, 119 figures, 4 tables, to appear in ApJ
CMB observations using the SKA
We examine the prospects for observations of CMB anisotropy with the SKA; we
discuss the advantages of interferometric SKA imaging, observing strategies,
calibration issues and the achievable sensitivity. Although the SKA will
probably operate at cm wavelengths, where discrete source confusion dominates
the CMB anisotropy, its extreme sensitivity to point sources will make it
possible to subtract the source contamination at these wavelengths and thereby
image the low surface brightness CMB anisotropies on small angular scales. The
SKA, operating at 10-20 GHz, may usefully make high-l observations of the CMB
anisotropy spectrum and survey the sky for Sunyaev-Zeldovich decrements.Comment: 4 pages. invited talk presented at the XXVIIth General Assembly of
the URSI, 17-24 Aug 2002, Maastricht, The Netherland
A novel technique for wide-field polarimetry with a radiotelescope array
We report the use of the Australia Telescope Compact Array (ATCA) to conduct
polarimetric observations of the sky at 5 GHz. The ATCA is normally operated as
an interferometer array, but these observations were conducted in a split array
mode in which the antenna elements were used as single-dishes with their beams
staggered to simultaneously cover a wide area of sky with a resolution of 10
arcmin. The linearly polarized sky radiation was fully characterized from
measurements, made over a range of parallactic angles, of the cross correlated
signals from the orthogonal linear feeds. We describe the technique and present
a polarimetric image of the Vela supernova remnant made as a test of the
method. The development of the techniques was motivated by the need for
wide-field imaging of the foreground contamination of the polarized component
of the cosmic microwave background signal.Comment: 13 pages, 2 figures, accepted for publication in A
The Abundance of X-Shaped Radio Sources: Implications for the Gravitational Wave Background
Coalescence of super massive black holes (SMBH's) in galaxy mergers is
potentially the dominant contributor to the low frequency gravitational wave
background (GWB). IIt was proposed by Merritt and Ekers (2002) that X-shaped
radio galaxies are signposts of such coalescences, and that their abundance
might be used to predict the magnitude of the gravitational wave background. In
Roberts et al. (2015) we present radio images of all 52 X-shaped radio source
candidates out of the sample of 100 selected by Cheung (2007) for which
archival VLA data were available. These images indicate that at most 21% of the
candidates might be genuine X-shaped radio sources that were formed by a
restarting of beams in a new direction following a major merger. This suggests
that fewer than 1.3% of extended radio sources appear to be candidates for
genuine axis reorientations ("spin flips"), much smaller than the 7% suggested
by Leahy and Parma (1992). Thus the associated gravitational wave background
may be substantially smaller than previous estimates. These results can be used
to normalize detailed calculations of the SMBH coalescence rate and the GWB
On the life-history and ecology of Hornellia marina gen. et sp. nov., (chloromonadineae), causing green discoloration of the sea and mortality among marine organisms off the Malabar coast
There are many published accounts dealing with " red ", " yellow " and
" pink " discoloration of the sea water, caused by the occurrence in swarms
of micro-organisms, particularly members of the Dinophyceae (cf. Hayes
and Austin, 1951). Some of these organisms are known to affect the fishery
adversely. Green discoloration of the sea, however, has not been recorded
frequently. Swarms of Noctiluca harbouring a green flagellate have been
recorded as having rendered the sea green by Weber and Weber van-Bosse
(1890), Delsman (1939-40), Prasad (1953) and recently by Subrahmanyan
(1953)
A new member of the Eugleninele, Protoeuglena noctilucae Gen. et sp. Nov., occurring in Noctiluca miliaris Suriray, causing green discoloration of the sea off Calicut
The presence of small green flagellates inside Noctiluca appears to have been first recorded by Weber and Weber-van Bosse (1890) who, however, did not observe the living material
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