118649031
Sunyaev-Zel'dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager
We present observations using the Small Array of the Arcminute Microkelvin Imager (AMI; 14–18 GHz) of four Abell and three MACS clusters spanning 0.171–0.686 in redshift. We detect Sunyaev–Zel’dovich (SZ) signals in five of these without any attempt at source subtraction, although strong source contamination is present. With radio-source measurements from high-resolution observations, and under the assumptions of spherical β-model, isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in the visibility plane detects extended SZ decrements in all seven clusters over and above receiver noise, radio sources and primary cosmic microwave background imprints. Formal Bayesian evidence ratios range from 1011:1 to 1043:1 for six of the clusters and 3000:1 for one with substantially fewer data than the others. We present posterior probability distributions for, e.g., total mass and gas fraction averaged over radii internal to which the mean overdensity is 1000, 500 and 200, r200 being the virial radius. Reaching r200 involves some extrapolation for the nearer clusters but not for the more distant ones. We find that our estimates of gas fraction are low (compared with most in the literature) and decrease with increasing radius. These results appear to be consistent with the notion that gas temperature in fact falls with distance (away from near the cluster centre) out to the virial radius.
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.
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.
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.
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.
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.
118657185
Dark matter CMB constraints and likelihoods for poor particle physicists
The cosmic microwave background provides constraints on the annihilation and decay of light dark matter at redshifts between 100 and 1000, the strength of which depends upon the fraction of energy ending up in the form of electrons and photons. The resulting constraints are usually presented for a limited selection of annihilation and decay channels. Here we provide constraints on the annihilation cross section and decay rate, at discrete values of the dark matter mass m{sub χ}, for all the annihilation and decay channels whose secondary spectra have been computed using PYTHIA in arXiv:1012.4515 (''PPPC 4 DM ID: a poor particle physicist cookbook for dark matter indirect detection''), namely e, μ, τ, V → e, V → μ, V → τ, u, d s, c, b, t, γ, g, W, Z and h. By interpolating in mass, these can be used to find the CMB constraints and likelihood functions from WMAP7 and Planck for a wide range of dark matter models, including those with annihilation or decay into a linear combination of different channels.
17921922
The Chemical Composition of the Sun
The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...
16965260
ON THE SOLAR NICKEL AND OXYGEN ABUNDANCES
Determinations of the solar oxygen content relying on the neutral forbidden transition at 630 nm depend upon the nickel abundance, due to a Ni I blend. Here, we rederive the solar nickel abundance, using the same ab initio three-dimensional hydrodynamic model of the solar photosphere employed in the recent revision of the abundances of C, N, O, and other elements. Using 17 weak, unblended lines of Ni I together with the most accurate atomic and observational data available, we find log Ni = 6.17 ± 0.02(statistical) ± 0.05(systematic), a downward shift of 0.06-0.08 dex relative to previous abundances based on one-dimensional model atmospheres. We investigate the implications of the new nickel abundance for studies of the solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun. Furthermore, we demonstrate that the oxygen abundance implied by the recent sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be revised downward from log O = 8.86 ± 0.07 to 8.71 ± 0.10. This revision is based on the new nickel abundance, the application of the best available gf value for the 630 nm forbidden oxygen line, and a more transparent treatment of CO formation. Determinations of the solar oxygen content relying on forbidden lines now appear to converge around log O = 8.7.
118475756
The elemental composition of the Sun - II. The iron group elements Sc to Ni
We redetermine the abundances of all iron group nuclei in the Sun, based on neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere, corrections for departures from local thermodynamic equilibrium (NLTE), stringent line selection procedures and high quality observational data. We have scoured the literature for the best quality oscillator strengths, hyperfine constants and isotopic separations available for our chosen lines. We find log ∈ = 3.16 ± 0.04, log ∈ = 4.93 ± 0.04, log ∈ = 3.89 ± 0.08, log ∈ = 5.62 ± 0.04, log ∈ = 5.42 ± 0.04, log ∈ = 7.47 ± 0.04, log ∈ = 4.93 ± 0.05 and log ∈ = 6.20 ± 0.04. Our uncertainties factor in both statistical and systematic errors (the latter estimated for possible errors in the model atmospheres and NLTE line formation). The new abundances are generally in good agreement with the CI meteoritic abundances but with some notable exceptions. This analysis constitutes both a full exposition and a slight update of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data we employed.
54675242
Impacts of Dark Stars on Reionization and Signatures in the Cosmic Microwave Background
We perform a detailed and systematic investigation of the possible impacts of dark stars on the reionization history of the universe, and its signatures in the cosmic microwave background (CMB). We compute hydrogen reionization histories, CMB optical depths, and anisotropy power spectra for a range of stellar populations including dark stars. If dark stars capture large amounts of dark matter (DM) via nuclear scattering, reionization can be substantially delayed, leading to decreases in the integrated optical depth to last scattering and large-scale power in the EE polarization power spectrum. Using the integrated optical depth observed by the Wilkinson Microwave Anistropy Probe seven-year mission, in our canonical reionization model we rule out the section of parameter space where dark stars with high scattering-induced capture rates tie up 90% of all the first star-forming baryons, and live for 250 Myr. When nuclear scattering delivers only moderate amounts of DM, reionization can instead be sped up slightly, modestly increasing the CMB optical depth. If dark stars do not obtain any DM via nuclear scattering, effectsonreionizationandtheCMBarenegligible.TheeffectsofdarkstarsonreionizationanditsCMBmarkerscan be largely mimicked or compensated for by changes in the existing parameters of reionization models, making dark stars difficult to disentangle from astrophysical uncertainties, but also widening the range of standard parameters in reionization models that can be made consistent with observations.