45 research outputs found
A VSA search for the extended Sunyaev-Zel'dovich Effect in the Corona Borealis Supercluster
We present interferometric imaging at 33 GHz of the Corona Borealis
supercluster, using the extended configuration of the Very Small Array. A total
area of 24 deg^2 has been imaged, with an angular resolution of 11 arcmin and a
sensitivity of 12 mJy/beam. The aim of these observations is to search for
Sunyaev-Zel'dovich (SZ) detections from known clusters of galaxies in this
supercluster and for a possible extended SZ decrement due to diffuse warm/hot
gas in the intercluster medium. We measure negative flux values in the
positions of the ten richest clusters in the region. Collectively, this implies
a 3.0-sigma detection of the SZ effect. In the clusters A2061 and A2065 we find
decrements of approximately 2-sigma. Our main result is the detection of two
strong and resolved negative features at -70+-12 mJy/beam (-157+-27 microK) and
-103+-10 mJy/beam (-230+-23 microK), respectively, located in a region with no
known clusters, near the centre of the supercluster. We discuss their possible
origins in terms of primordial CMB anisotropies and/or SZ signals related to
either unknown clusters or to a diffuse extended warm/hot gas distribution. Our
analyses have revealed that a primordial CMB fluctuation is a plausible
explanation for the weaker feature (probability of 37.82%). For the stronger
one, neither primordial CMB (probability of 0.33%) nor SZ can account alone for
its size and total intensity. The most reasonable explanation, then, is a
combination of both primordial CMB and SZ signal. Finally, we explore what
characteristics would be required for a filamentary structure consisting of
warm/hot diffuse gas in order to produce a significant contribution to such a
spot taking into account the constraints set by X-ray data.Comment: 16 pages, 10 figures. Accepted in MNRA
First results from the Very Small Array -- III. The CMB power spectrum
We present the power spectrum of the fluctuations in the cosmic microwave
background detected by the Very Small Array (VSA) in its first season of
observations in its compact configuration. We find clear detections of first
and second acoustic peaks at l~200 and l~550, plus detection of power on scales
up to l=800. The VSA power spectrum is in very good agreement with the results
of the Boomerang, Dasi and Maxima telescopes despite the differing potential
systematic errors.Comment: 10 pages, 6 figure, MNRAS in press. (Minor revisions - accepted 17
December 2002
First results from the Very Small Array -- II. Observations of the CMB
We have observed the cosmic microwave background temperature fluctuations in
eight fields covering three separated areas of sky with the Very Small Array at
34 GHz. A total area of 101 square degrees has been imaged, with sensitivity on
angular scales 3.6 - 0.4 degrees (equivalent to angular multipoles l=150-900).
We describe the field selection and observing strategy for these observations.
In the full-resolution images (with synthesised beam of FWHM ~ 17 arcmin) the
thermal noise is typically 45 microK and the CMB signal typically 55 microK.
The noise levels in each field agree well with the expected thermal noise level
of the telescope, and there is no evidence of any residual systematic features.
The same CMB features are detected in separate, overlapping observations.
Discrete radio sources have been detected using a separate 15 GHz survey and
their effects removed using pointed follow-up observations at 34 GHz. We
estimate that the residual confusion noise due to unsubtracted radio sources is
less than 14 mJy/beam (15 microK in the full-resolution images), which added in
quadrature to the thermal noise increases the noise level by 6 %. We estimate
that the rms contribution to the images from diffuse Galactic emission is less
than 6 microK. We also present images which are convolved to maximise the
signal-to-noise of the CMB features and are co-added in overlapping areas, in
which the signal-to-noise of some individual CMB features exceeds 8.Comment: 11 pages, 5 figures, accepted for publication in MNRAS. Replaces
original version - more detailed abstract, corrected typo
Non-Gaussianity in the Very Small Array CMB maps with Smooth-Goodness-of-fit tests
(Abridged) We have used the Rayner & Best (1989) smooth tests of
goodness-of-fit to study the Gaussianity of the Very Small Array (VSA) data.
Out of the 41 published VSA individual pointings dedicated to cosmological
observations, 37 are found to be consistent with Gaussianity, whereas four
pointings show deviations from Gaussianity. In two of them, these deviations
can be explained as residual systematic effects of a few visibility points
which, when corrected, have a negligible impact on the angular power spectrum.
The non-Gaussianity found in the other two (adjacent) pointings seems to be
associated to a local deviation of the power spectrum of these fields with
respect to the common power spectrum of the complete data set, at angular
scales of the third acoustic peak (l = 700-900). No evidence of residual
systematics is found in this case, and unsubstracted point sources are not a
plausible explanation either. If those visibilities are removed, a cosmological
analysis based on this new VSA power spectrum alone shows no differences in the
parameter constraints with respect to our published results, except for the
physical baryon density, which decreases by 10 percent. Finally, the method has
been also used to analyse the VSA observations in the Corona Borealis
supercluster region (Genova-Santos et al. 2005), which show a strong decrement
which cannot be explained as primordial CMB. Our method finds a clear deviation
(99.82%) with respect to Gaussianity in the second-order moment of the
distribution, and which can not be explained as systematic effects. A detailed
study shows that the non-Gaussianity is produced in scales of l~500, and that
this deviation is intrinsic to the data (in the sense that can not be explained
in terms of a Gaussian field with a different power spectrum).Comment: 14 pages, 7 figures. Accepted for publication in MNRA
The CMB power spectrum out to l=1400 measured by the VSA
We have observed the cosmic microwave background (CMB) in three regions of
sky using the Very Small Array (VSA) in an extended configuration with antennas
of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA
observations using a more compact array with larger beamwidth, we measure the
power spectrum of the primordial CMB anisotropies between angular multipoles l
= 160 - 1400. Such measurements at high l are vital for breaking degeneracies
in parameter estimation from the CMB power spectrum and other cosmological
data. The power spectrum clearly resolves the first three acoustic peaks, shows
the expected fall off in power at high l and starts to constrain the position
and height of a fourth peak.Comment: 6 pages with 5 figures, MNRAS in press (minor corrections
PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky
PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to
ESA in response to the Call for White Papers for the definition of the L2 and
L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1)
an imager with a 3.5m mirror (cooled to 4K for high performance in the
far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and
(2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS
instrument but over three orders of magnitude more sensitive. Highlights of the
new science (beyond the obvious target of B-modes from gravity waves generated
during inflation) made possible by these two instruments working in tandem
include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters
extending to large redshift and measuring their peculiar velocities and
temperatures (through the kSZ effect and relativistic corrections to the
classic y-distortion spectrum, respectively) (2) a detailed investigation into
the nature of the cosmic infrared background (CIB) consisting of at present
unresolved dusty high-z galaxies, where most of the star formation in the
universe took place, (3) searching for distortions from the perfect CMB
blackbody spectrum, which will probe a large number of otherwise inaccessible
effects (e.g., energy release through decaying dark matter, the primordial
power spectrum on very small scales where measurements today are impossible due
to erasure from Silk damping and contamination from non-linear cascading of
power from larger length scales). These are but a few of the highlights of the
new science that will be made possible with PRISM.Comment: 20 pages Late