10867413
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 2×2 deg2 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 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 =422 (θ≈51 arcmin) is estimated to be . For multipoles centred on l=615 (θ≈35 arcmin), we find contamination from Galactic emission is significant, and constrain the CMB contribution to the measured power in this bin to be ΔTT<2.0×10−5 (1σ 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 deg. Improved limits on the values of H0 and Ω are determined using the new CAT data.
118516213
Sunyaev-Zel'dovich observations of LoCuSS clusters with the Arcminute Microkelvin Imager: high X-ray luminosity sample
We present observations from the Small Array of the Arcminut e Microkelvin Imager (AMI) of eight high X-ray luminosity galaxy cluster systems selec ted from the Local Cluster Substructure Survey (LoCuSS) sample. We detect the Sunyaev-Ze l’dovich (SZ) effect in seven of these clusters. With the assumptions that galaxy clusters a r i othermal, have a density profile described by a spherical β -model and obey the theoretical M-T relation, we are able to d erive cluster parameters at r200 from our SZ data. With the additional assumption of hydrosta tic equilibrium we are able to derive parameters at r500. We present posterior probability distributions for cluster parameters such as mass, radius and temp erature ( TSZ,MT ). Combining our sample with that of AMI Consortium: Rodrı́guez-Gonzálvez et al. (2011) and using largeradius X-ray temperature estimates ( TX ) from Chandra andSuzaku observations, we find that there is reasonable correspondence between TX andTSZ,MT values at lowTX , but that for clusters withTX above around 6keV the correspondence breaks down with TX exceedingTSZ,MT ; we stress that this finding is based on just ten clusters.
13613140
AMI observations of Lynds dark nebulae: Further evidence for anomalous cm-wave emission
Observations at 14.2 to 17.9 GHz made with the Arcminute Microkelvin Imager (AMI) Small Array towards 14 Lynds dark nebulae with a resolution of ≈2 arcmin are reported. These sources are selected from the Submillimetre Common-User Bolometre Array (SCUBA) observations of Visser, Richer & Chandler as small angular diameter clouds well matched to the synthesized beam of the AMI Small Array. Comparison of the AMI observations with radio observations at lower frequencies with matched uv-plane coverage is made, in order to search for any anomalous excess emission which can be attributed to spinning dust. Possible emission from spinning dust is identified as a source within a 2-arcmin radius of the SCUBA position of the Lynds dark nebula, exhibiting an excess with respect to lower frequency radio emission. We find five sources which show a possible spinning dust component in their spectra. These sources have rising spectral indices in the frequency range 14.2–17.9 GHz with α 17.9 14.2 =− 0.7 ± 0.7 to −2.9 ± 0.4, where S ∝ ν −α . Of these five one has already been reported, L1111, we report one new definite detection, L675 (16σ ), and three new probable detections (L944, L1103 and L1246). The relative certainty of these detections is assessed on the basis of three criteria: the extent of the emission, the coincidence of the emission with the SCUBA position and the likelihood of alternative explanations for the excess. Extended microwave emission makes the likelihood of the anomalous emission arising as a consequence of a radio counterpart to a protostar or a protoplanetary disc unlikely. We use a 2-arcmin radius in order to be consistent with the IRAS identifications of dark nebulae, and our third criterion is used in the case of L1103 where a high flux density at 850 μm relative to the far-infrared data suggests a more complicated emission spectrum.
1866023
AMI Galactic Plane Survey at 16 GHz – I. Observing, mapping and source extraction
The Arcminute Microkelvin Imager (AMI) Galactic Plane Survey is a large-area survey of the outer Galactic plane to provide arcminute resolution images at milli-Jansky sensitivity in the centimetre-wave band. Here we present the first data release of the survey, consisting of 868 deg^2 of the Galactic plane, covering the area 76° ⪅ l ⪅ 170° between latitudes of |b| ⪅ 5°, at a central frequency of 15.75 GHz (1.9 cm). We describe in detail the drift-scan observations which have been used to construct the maps, including the techniques used for observing, mapping and source extraction, and summarize the properties of the finalized data sets. These observations constitute the most sensitive Galactic plane survey of large extent at centimetre-wave frequencies greater than 1.4 GHz.
18950684
The Very Small Array - status report
We are contructing an interferometric telescope, the Very Small Array, to study the cosmic microwave background on angular scales 0.2--4.5 degrees. The physical layout and electronic design of the telescope are optimised to give maximum protection from systematic effects, while still providing sufficient sensitivity to make high signal-to-noise images. A prototype single baseline is currently being tested, with scientific results expected during 2000.
7640204
A blind detection of a large, complex, Sunyaev–Zel’dovich structure★
We present an interesting Sunyaev–Zel’dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) ‘blind’, degree-square fields to have been observed down to our target sensitivity of 100µJy beam^(-1). In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than eight times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (≈10 arcmin) and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal or spherical β model, which does not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. approximation to Press & Schechter correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the formal Bayesian probability ratio of the AMI detection of this cluster is 7.9 × 10^4:1; alternatively assuming Jenkins et al. as the true prior, the formal Bayesian probability ratio of detection is 2.1 × 10^5:1. (b) The cluster mass is M_(T,200) = 5.5_(-1.3)^(+1.2) x 10^(14)h^(-1)_(70) M_☉. (c) Abandoning a physical model with number density prior and instead simply modelling the SZ decrement using a phenomenological β model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of -295_(-15)^(+36) µK – this allows for cosmic microwave background primary anisotropies, receiver noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters.
119276783
FINDING HIGH-REDSHIFT DARK STARS WITH THE JAMES WEBB SPACE TELESCOPE
The first stars in the history of the universe are likely to form in the dense central regions of similar to 10(5)-10(6) M-circle dot cold dark matter halos at z approximate to 10-50. The annihilat ...
119301431
Number counts and non-Gaussianity
We describe a general procedure for using number counts of any object to constrain the probability distribution of the primordial fluctuations, allowing for generic weak non-Gaussianity. We apply this procedure to use limits on the abundance of primordial black holes and dark matter ultracompact minihalos (UCMHs) to characterize the allowed statistics of primordial fluctuations on very small scales. We present constraints on the power spectrum and the amplitude of the skewness for two different families of non-Gaussian distributions, distinguished by the relative importance of higher moments. Although primordial black holes probe the smallest scales, ultracompact minihalos provide significantly stronger constraints on the power spectrum and so are more likely to eventually provide small-scale constraints on non-Gaussianity.
67761008
Detection of isolated Population III stars with the James Webb Space Telescope
The first Population III stars are predicted to form in minihaloes at z approximate to 10-30. The James Webb Space Telescope (JWST), tentatively scheduled for launch in 2018, will probably be able ...
118637683
Thermal conduction by dark matter with velocity and momentum-dependent cross-sections
We use the formalism of Gould and Raffelt [1] to compute the dimensionless thermal conduction coefficients for scattering of dark matter particles with standard model nucleons via cross-sections that depend on the relative velocity or momentum exchanged between particles. Motivated by models invoked to reconcile various recent results in direct detection, we explicitly compute the conduction coefficients α and κ for cross-sections that go as v{sub rel}{sup 2}, v{sub rel}{sup 4}, v{sub rel}{sup −2}, q{sup 2}, q{sup 4} and q{sup −2}, where v{sub rel} is the relative DM-nucleus velocity and q is the momentum transferred in the collision. We find that a v{sub rel}{sup −2} dependence can significantly enhance energy transport from the inner solar core to the outer core. The same can true for any q-dependent coupling, if the dark matter mass lies within some specific range for each coupling. This effect can complement direct searches for dark matter; combining these results with state-of-the-art solar simulations should greatly increase sensitivity to certain DM models. It also seems possible that the so-called Solar Abundance Problem could be resolved by enhanced energy transport in the solar core due to such velocity- or momentum-dependent scatterings.
1373212
Sensitivity of CTA to dark matter signals from the Galactic Center
The Galactic Center is one of the most promising targets for indirect detection of dark matter with gamma rays. We investigate the sensitivity of the upcoming Cherenkov Telescope Array (CTA) to dark matter annihilation and decay in the Galactic Center. As the inner density profile of the Milky Way's dark matter halo is uncertain, we study the impact of the slope of the Galactic density profile, inwards of the Sun, on the prospects for detecting a dark matter signal with CTA. Adopting the Ring Method to define the signal and background regions in an ON-OFF analysis approach, we find that the sensitivity achieved by CTA to annihilation signals is strongly dependent on the inner profile slope, whereas the dependence is more mild in the case of dark matter decay. Surprisingly, we find that the optimal choice of signal and background regions is virtually independent of the assumed density profile. For the fiducial case of a Navarro-Frenk-White profile, we find that CTA will be able to probe annihilation cross sections well below the canonical thermal relic value for dark matter masses from a few tens of GeV up to 5 TeV for annihilation to + , and will achieve only a slightly weaker sensitivity for annihilation to b b or + . CTA will improve significantly on current sensitivity to annihilation signals for dark matter masses above 100 GeV, covering parameter space that is complementary to that probed by searches with the Fermi Large Area Telescope. The interpretation of apparent excesses in the measured cosmic-ray electron and positron spectra as signals of dark matter decay will also be testable with CTA observations of the Galactic Center. We demonstrate that both for annihilation and for decay, including spectral information for hard channels (such as + and + ) leads to enhanced sensitivity for dark matter masses above mDM 200 GeV.