37 research outputs found
Constraining dark energy with Sunyaev-Zel'dovich cluster surveys
We discuss the prospects of constraining the properties of a dark energy
component, with particular reference to a time varying equation of state, using
future cluster surveys selected by their Sunyaev-Zel'dovich effect. We compute
the number of clusters expected for a given set of cosmological parameters and
propogate the errors expected from a variety of surveys. In the short term they
will constrain dark energy in conjunction with future observations of type Ia
supernovae, but may in time do so in their own right.Comment: 5 pages, 3 figures, 1 table, version accepted for publication in PR
Using ALMA to resolve the nature of the early star-forming large-scale structure PLCK G073.4-57.5
Galaxy clusters at high redshift are key targets for understanding matter
assembly in the early Universe, yet they are challenging to locate. A sample of
>2000 high-z candidate structures has been found using Planck's all-sky submm
maps, and a sub-set of 234 have been followed up with Herschel-SPIRE, which
showed that the emission can be attributed to large overdensities of dusty
star-forming galaxies. In order to resolve and characterise the individual
galaxies we targeted the eight brightest SPIRE sources in the centre of the
Planck peak PLCK G073.4-57.5 using ALMA at 1.3 mm, and complemented these
observations with data from IRAC, WIRCam J,K, and SCUBA-2. We detected a total
of 18 millimetre galaxies brighter than 0.3 mJy in 2.4 arcmin^2. The ALMA
source density is 8-30 times higher than average background estimates and
larger than seen in typical 'proto-cluster' fields. We were able to match all
but one of the ALMA sources to a NIR counterpart. The most significant (four)
SCUBA-2 sources are not included in the ALMA pointings, but we find an 8sigma
stacking detection of the ALMA sources in the SCUBA-2 map at 850 um. We derive
photo-z, L_IR, SFR, stellar mass, T_dust, M_dust for all of the ALMA galaxies;
the photo-zs identify two groups each of five sources, at z~1.5 and 2.4. The
two groups show two 'red sequences' (i.e. similar NIR [3.6]-[4.5] colours and
different J-K colours). The majority of the ALMA-detected galaxies are on the
SFR versus stellar mass main sequence, and half of the sample is more massive
than the characteristic stellar mass at the corresponding redshift.
Serendipitous CO line detections in two of the galaxies appear to match their
photometric redshifts at z~1.54. We performed an analysis of star-formation
efficiencies and CO- and mm-continuum-derived gas fractions of our ALMA
sources, combined with a sample of 1<z<3 cluster and proto-cluster members.Comment: 26 pages, revised version, Astronomy & Astrophysics accepte
Searching for non-Gaussianity in the VSA data
We have tested Very Small Array (VSA) observations of three regions of sky
for the presence of non-Gaussianity, using high-order cumulants, Minkowski
functionals, a wavelet-based test and a Bayesian joint power
spectrum/non-Gaussianity analysis. We find the data from two regions to be
consistent with Gaussianity. In the third region, we obtain a 96.7% detection
of non-Gaussianity using the wavelet test. We perform simulations to
characterise the tests, and conclude that this is consistent with expected
residual point source contamination. There is therefore no evidence that this
detection is of cosmological origin. Our simulations show that the tests would
be sensitive to any residual point sources above the data's source subtraction
level of 20 mJy. The tests are also sensitive to cosmic string networks at an
rms fluctuation level of (i.e. equivalent to the best-fit observed
value). They are not sensitive to string-induced fluctuations if an equal rms
of Gaussian CDM fluctuations is added, thereby reducing the fluctuations due to
the strings network to rms . We especially highlight the usefulness
of non-Gaussianity testing in eliminating systematic effects from our data.Comment: Minor corrections; accepted for publication to MNRA
Estimating the bispectrum of the Very Small Array data
We estimate the bispectrum of the Very Small Array data from the compact and
extended configuration observations released in December 2002, and compare our
results to those obtained from Gaussian simulations. There is a slight excess
of large bispectrum values for two individual fields, but this does not appear
when the fields are combined. Given our expected level of residual point
sources, we do not expect these to be the source of the discrepancy. Using the
compact configuration data, we put an upper limit of 5400 on the value of f_NL,
the non-linear coupling parameter, at 95 per cent confidence. We test our
bispectrum estimator using non-Gaussian simulations with a known bispectrum,
and recover the input values.Comment: 17 pages, 16 figures, replaced with version accepted by MNRAS.
Primordial bispectrum recalculated and figure 11 change
Mapping of the SZ effect in the cluster Cl 0016+16 with the Ryle Telescope
We have mapped the high-redshift (z = 0.546) cluster Cl 0016+16 with the Ryle
Telescope at 15 GHz. The Sunyaev-Zel'dovich decrement is clearly detected, and
resolved. We combine our data with an X-ray image from ROSAT, and a gas
temperature from ASCA to estimate the Hubble Constant H0 = 69 +21/-16 km/s/Mpc
for an Omega_M=1.0 cosmology or H0 = 84 +25/-19 km/s/Mpc for Omega_M=0.3 and
Omega_Lambda=0.7.Comment: 10 pages, 2 tables, 6 figures Submitted to MNRA
Source subtraction for the extended Very Small Array and 33-GHz source count estimates
We describe the source subtraction strategy and observations for the extended
Very Small Array, a CMB interferometer operating at 33 GHz. A total of 453
sources were monitored at 33 GHz using a dedicated source subtraction baseline.
131 sources brighter than 20 mJy were directly subtracted from the VSA
visibility data. Some characteristics of the subtracted sources, such as
spectra and variability, are discussed. The 33-GHz source counts are estimated
from a sample selected at 15 GHz. The selection of VSA fields in order to avoid
bright sources introduces a bias into the observed counts. This bias is
corrected and the resulting source count is estimated to be complete in the
flux-density range 20-114 mJy. The 33-GHz source counts are used to calculate a
correction to the VSA power spectrum for sources below the subtraction limit.Comment: 15 pages, 15 figures, submitted to MNRA
CMB observations from the CBI and VSA: A comparison of coincident maps and parameter estimation methods
We present coincident observations of the Cosmic Microwave Background (CMB)
from the Very Small Array (VSA) and Cosmic Background Imager (CBI) telescopes.
The consistency of the full datasets is tested in the map plane and the Fourier
plane, prior to the usual compression of CMB data into flat bandpowers. Of the
three mosaics observed by each group, two are found to be in excellent
agreement. In the third mosaic, there is a 2 sigma discrepancy between the
correlation of the data and the level expected from Monte Carlo simulations.
This is shown to be consistent with increased phase calibration errors on VSA
data during summer observations. We also consider the parameter estimation
method of each group. The key difference is the use of the variance window
function in place of the bandpower window function, an approximation used by
the VSA group. A re-evaluation of the VSA parameter estimates, using bandpower
windows, shows that the two methods yield consistent results.Comment: 10 pages, 6 figures. Final version. Accepted for publication in MNRA
A Very Small Array 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 deg² has been imaged, with an angular resolution of 11 arcmin and a sensitivity of 12 mJy beam⁻¹. 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. Hydrodynamical simulations suggest that a significant part of the missing baryons in the Local Universe may be located in superclusters.
The maps constructed from these observations have a significant contribution from primordial fluctuations. We measure negative flux values in the positions of the 10 richest clusters in the region. Collectively, this implies a 3.0σ detection of the SZ effect. For two of these clusters, A2061 and A2065, we find decrements of approximately 2σ each.
Our main result is the detection of two strong and resolved negative features at −70 ± 12 mJy beam⁻¹ (−157 ± 27 μK) and −103 ± 10 mJy beam⁻¹ (−230 ± 23 μK), respectively, located in a region with no known clusters, near the centre of the supercluster. We discuss their possible origins in terms of primordial cosmic microwave background (CMB) anisotropies and/or SZ signals related either to 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 per cent). For the stronger one, neither primordial CMB (probability of 0.38 per cent) 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
A Very Small Array 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 deg² has been imaged, with an angular resolution of 11 arcmin and a sensitivity of 12 mJy beam⁻¹. 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. Hydrodynamical simulations suggest that a significant part of the missing baryons in the Local Universe may be located in superclusters.
The maps constructed from these observations have a significant contribution from primordial fluctuations. We measure negative flux values in the positions of the 10 richest clusters in the region. Collectively, this implies a 3.0σ detection of the SZ effect. For two of these clusters, A2061 and A2065, we find decrements of approximately 2σ each.
Our main result is the detection of two strong and resolved negative features at −70 ± 12 mJy beam⁻¹ (−157 ± 27 μK) and −103 ± 10 mJy beam⁻¹ (−230 ± 23 μK), respectively, located in a region with no known clusters, near the centre of the supercluster. We discuss their possible origins in terms of primordial cosmic microwave background (CMB) anisotropies and/or SZ signals related either to 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 per cent). For the stronger one, neither primordial CMB (probability of 0.38 per cent) 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