549 research outputs found
Investigating the source of Planck-detected AME: high resolution observations at 15 GHz
The Planck 28.5 GHz maps were searched for potential Anomalous Microwave
Emission (AME) regions on the scale of or smaller, and several
new regions of interest were selected. Ancillary data at both lower and higher
frequencies were used to construct spectral energy distributions (SEDs), which
seem to confirm an excess consistent with spinning dust models. Here we present
higher resolution observations of two of these new regions with the Arcminute
Microkelvin Imager Small Array (AMI SA) between 14 and 18 GHz to test for the
presence of a compact (10 arcmin or smaller) component. For
AME-G107.1+5.2, dominated by the {\sc Hii} region S140, we find evidence for
the characteristic rising spectrum associated with the either the spinning dust
mechanism for AME or an ultra/hyper-compact \textsc{Hii} region across the AMI
frequency band, however for AME-G173.6+2.8 we find no evidence for AME on
scales of arcmin.Comment: 13 pages, 8 figures, 4 tables. Submitted to Advances in Astronomy AME
Special Issu
Observing the CMB at High-l using the VSA and AMI
We discuss two experiments - the Very Small Array (VSA) and the Arcminute
MicroKelvin Imager (AMI) - and their prospects for observing the CMB at high
angular multipoles. Whilst the VSA is primarily designed to observe primary
anisotropies in the CMB, AMI is designed to image secondary anisotropies via
the Sunyaev-Zel'dovich effect. The combined l-range of these two instruments is
between l = 150 and ~10000.Comment: 8 pages, 13 figures. To be published in the proceedings of "The
Cosmic Microwave Background and its Polarization", New Astronomy Reviews,
(eds. S. Hanany and K.A. Olive
CLOVER - A new instrument for measuring the B-mode polarization of the CMB
We describe the design and expected performance of Clover, a new instrument
designed to measure the B-mode polarization of the cosmic microwave background.
The proposed instrument will comprise three independent telescopes operating at
90, 150 and 220 GHz and is planned to be sited at Dome C, Antarctica. Each
telescope will feed a focal plane array of 128 background-limited detectors and
will measure polarized signals over angular multipoles 20 < l < 1000. The
unique design of the telescope and careful control of systematics should enable
the B-mode signature of gravitational waves to be measured to a
lensing-confusion-limited tensor-to-scalar ratio r~0.005.Comment: 4 pages, 5 figures. To appear in the proceedings of the XXXVIXth
Rencontres de Moriond "Exploring the Universe
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
Detection of Cosmic Microwave Background Structure in a Second Field with the Cosmic Anisotropy Telescope
We describe observations at frequencies near 15 GHz of the second 2x2 degree
field imaged with the Cambridge Cosmic Anisotropy Telescope (CAT). After the
removal of discrete radio sources, structure is detected in the images on
characteristic scales of about half a degree, corresponding to spherical
harmonic multipoles in the approximate range l= 330--680. A Bayesian analysis
confirms that the signal arises predominantly from the cosmic microwave
background (CMB) radiation for multipoles in the lower half of this range; the
average broad-band power in a bin with centroid l=422 (theta = 51') is
estimated to be Delta_T/T=2.1^{+0.4}_{-0.5} x 10^{-5}. For multipoles centred
on l=615 (theta =35'), we find contamination from Galactic emission is
significant, and constrain the CMB contribution to the measured power in this
bin to be Delta_T/T <2.0 x 10^{-5} (1-sigma upper limit). These new results are
consistent with the first detection made by CAT in a completely different area
of sky. Together with data from other experiments, this new CAT detection adds
weight to earlier evidence from CAT for a downturn in the CMB power spectrum on
scales smaller than 1 degree. Improved limits on the values of H_0 and Omega
are determined using the new CAT data.Comment: 5 pages, 5 figures (gif), submitted to MNRA
Galaxy Cluster Shapes and Systematic Errors in H0 Measured by the Sunyaev-Zel'dovich Effect
Imaging of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters combined
with cluster plasma x-ray diagnostics can measure the cosmic distance scale to
high redshift. Projecting the inverse-Compton scattering and x-ray emission
along the cluster line-of-sight introduces systematic errors in the Hubble
constant, H0, because the true shape of the cluster is not known. I present a
study of the systematic errors in the value of H0, as determined by the x-ray
and SZ properties of theoretical samples of triaxial isothermal ``beta'' model
clusters, caused by projection effects and observer orientation. I calculate
estimates for H0 for each cluster based on their large and small apparent
angular core radii and their arithmetic mean. I demonstrate that the estimates
for H0 for a sample of 25 clusters have 99.7% confidence intervals for the mean
estimated H0 analyzing the clusters using either their large or mean angular
core radius are within 14% of the ``true'' (assumed) value of H0 (and enclose
it), for a triaxial beta model cluster sample possessing a distribution of
apparent x-ray cluster ellipticities consistent with that of observed x-ray
clusters. This limit on the systematic error in H0 caused by cluster shape
assumes that each sample beta model cluster has fixed shape; deviations from
constant shape within the clusters may introduce additional uncertainty or bias
into this result.Comment: Accepted for publication in the Astrophysical Journal, 24 March 1998;
4 pages, 2 figure
A close-pair binary in a distant triple supermassive black-hole system
Galaxies are believed to evolve through merging, which should lead to
multiple supermassive black holes in some. There are four known triple black
hole systems, with the closest pair being 2.4 kiloparsecs apart (the third
component is more distant at 3 kiloparsecs), which is far from the
gravitational sphere of influence of a black hole with mass 10
M (about 100 parsecs). Previous searches for compact black hole systems
concluded that they were rare, with the tightest binary system having a
separation of 7 parsecs. Here we report observations of a triple black hole
system at redshift z=0.39, with the closest pair separated by 140
parsecs. The presence of the tight pair is imprinted onto the properties of the
large-scale radio jets, as a rotationally-symmetric helical modulation, which
provides a useful way to search for other tight pairs without needing extremely
high resolution observations. As we found this tight pair after searching only
six galaxies, we conclude that tight pairs are more common than hitherto
believed, which is an important observational constraint for low-frequency
gravitational wave experiments.Comment: 21 pages, 6 figures. Published online by Nature on 25 June 2014.
Extremely minor differences with published version exis
AMI SZ observation of galaxy-cluster merger CIZA J2242+5301: Perpendicular flows of gas and dark matter
© 2018 The Author(s). Arcminute Microkelvin Imager observations towards CIZA J2242+5301, in comparison with observations of weak gravitational lensing and X-ray emission from the literature, are used to investigate the behaviour of non-baryonic dark matter (NBDM) and gas during the merger. Analysis of the Sunyaev-Zel'dovich (SZ) signal indicates the presence of high pressure gas elongated perpendicularly to the X-ray and weak-lensing morphologies, which, given the merger-axis constraints in the literature, implies that high pressure gas is pushed out into a linear structure during core passing. Simulations in the literature closely matching the inferred merger scenario show the formation of gas density and temperature structures perpendicular to the merger axis. These SZ observations are challenging for modified gravity theories in which NBDM is not the dominant contributor to galaxy-cluster gravity.STFC (ST/M001172/1)
STFC (ST/K00333X/1)
STFC (ST/M007065/1)
STFC (ST/H008586/1)
STFC (ST/J005673/1
AMI galactic plane survey at 16 GHz - II. Full data release with extended coverage and improved processing
The Arcminute Microkelvin Imager Galactic Plane Survey (AMIGPS) provides
mJy-sensitivity, arcminute-resolution interferometric images of the northern
Galactic plane at 16 GHz. The first data release covered between latitudes of ; here we present a second data release, extending the coverage to
and including
high-latitude extensions to cover the Taurus and California giant molecular
cloud regions, and the recently discovered large supernova remnant G159.6+7.3.
The total coverage is now 1777 deg and the catalogue contains 6509 sources.
We also describe the improvements to the data processing pipeline which
improves the positional and flux density accuracies of the survey.We thank the staff of the Mullard Radio Astronomy Observatory for their invaluable assistance in the commissioning and operation of AMI, which is supported by Cambridge University and the Science and Technologies Facilities Council. YCP acknowledges support from a CCT/Cavendish Laboratory studentship and a Trinity College Junior Research Fellowship. CR and TZJ acknowledge support from Science and Technology Facilities Council studentships.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv172
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