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.
119289890
The elemental composition of the Sun I. The intermediate mass elements Na to Ca
The chemical composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geophysics: elemental abundances of essentially all astronomical objects are referenced to the solar composition, and basically every process involving the Sun depends on its composition. This article, dealing with the intermediate-mass elements Na to Ca, is the first in a series describing the comprehensive re-determination of the solar composition. In this series we severely scrutinise all ingredients of the analysis across all elements, to obtain the most accurate, homogeneous and reliable results possible. We employ a highly realistic 3D hydrodynamic model of the solar photosphere, which has successfully passed an arsenal of observational diagnostics. For comparison, and to quantify remaining systematic errors, we repeat the analysis using three different 1D hydrostatic model atmospheres (marcs, miss and Holweger & Muller 1974, Sol. Phys., 39, 19) and a horizontally and temporally-averaged version of the 3D model (〈3D〉). We account for departures from local thermodynamic equilibrium (LTE) wherever possible. We have scoured the literature for the best possible input data, carefully assessing transition probabilities, hyperfine splitting, partition functions and other data for inclusion in the analysis. We have put the lines we use through a very stringent quality check in terms of their observed profiles and atomic data, and discarded all that we suspect to be blended. Our final recommended 3D+NLTE abundances are: log e = 6:21 ± 0:04, log e = 7:59 ± 0:04, log e = 6:43 ± 0:04, log e = 7:51 ± 0:03, log e = 5:41 ± 0:03, log e = 7:13 ± 0:03, log e = 5:04 ± 0:05 and log e = 6:32 ± 0:03. The uncertainties include both statistical and systematic errors. Our results are systematically smaller than most previous ones with the 1D semi-empirical Holweger & Muller model, whereas the 〈3D〉 model returns abundances very similar to the full 3D calculations. This analysis provides a complete description and a slight update of the results presented in Asplund et al. (2009, ARA&A, 47, 481) for Na to Ca, and includes full details of all lines and input data used.
3586757
Fundamental statistical limitations of future dark matter direct detection experiments
We discuss irreducible statistical limitations of future ton-scale dark matter direct detection experiments. We focus in particular on the coverage of confidence intervals, which quantifies the reliability of the statistical method used to reconstruct the dark matter parameters and the bias of the reconstructed parameters. We study 36 benchmark dark matter models within the reach of upcoming ton-scale experiments. We find that approximate confidence intervals from a profile-likelihood analysis exactly cover or overcover the true values of the weakly interacting massive particle (WIMP) parameters, and hence are conservative. We evaluate the probability that unavoidable statistical fluctuations in the data might lead to a biased reconstruction of the dark matter parameters, or large uncertainties on the reconstructed parameter values. We show that this probability can be surprisingly large, even for benchmark models leading to a large event rate of order a hundred counts. We find that combining data sets from two different targets leads to improved coverage properties, as well as a substantial reduction of statistical bias and uncertainty on the dark matter parameters.
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.
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 ...
55777556
Pippi — Painless parsing, post-processing and plotting of posterior and likelihood samples
Abstract.Interpreting samples from likelihood or posterior probability density functions is rarely as straightforward as it seems it should be. Producing publication-quality graphics of these distributions is often similarly painful. In this short note I describe pippi, a simple, publicly available package for parsing and post-processing such samples, as well as generating high-quality PDF graphics of the results. Pippi is easily and extensively configurable and customisable, both in its options for parsing and post-processing samples, and in the visual aspects of the figures it produces. I illustrate some of these using an existing supersymmetric global fit, performed in the context of a gamma-ray search for dark matter. Pippi can be downloaded and followed at http://github.com/patscott/pippi.
118474158
Parameterization Effects in the analysis of Sunyaev-Zel'dovich Observations
Current studies of the Sunyaev-Zel'dovich (SZ) effect are based on parameterized models of galaxy clusters. Investigating the effects of different parameterizations and the assumptions made within any parameterized model are,therefore, crucial in extracting cluster physical properties in a robust way. In this paper, we study three different parameterizations of the well-studied isothermal beta-model applied to a simulated Arcminute Microkelvin Imager observation of a galaxy cluster through its SZ effect. We propose a method for generating simulated SZ data that leads to consistent values of cluster physical properties upon employing different parameterization methods. The results of our study clearly reveal different biases and constraints induced by each parameterization. We also find that the way in which conventional assumptions on the dynamical state of the gas and dark matter are applied to a parameterized cluster model play a significant role in both determining degeneracies and deriving apparent constraints. By comparing different parameterizations, we confirm the model parameters that cannot be constrained by SZ data alone. We also find that the assumption of isothermality when the cluster hot gas is in hydrostatic equilibrium with its total gravitational potential introduces clear biases in the posterior probability distributions of the cluster parameters, as the temperature gradient is eliminated from the analysis. However, our results show that by employing a scaling relation to link cluster total mass internal to the virial radius with mean temperature, we are able to obtain reliable results for extracting physical cluster parametes compared to the corresponding true input values in the simulation .
7401876
AMI limits on 15-GHz excess emission in northern H ii regions
We present observations between 14.2 and 17.9 GHz of 16 Galactic H ii regions made with the Arcminute Microkelvin Imager. In conjunction with data from the literature at lower radio frequencies we investigate the possibility of a spinning dust component in the spectra of these objects. We conclude that there is no significant evidence for spinning dust towards these sources and measure an average spectral index of ?= 0.15 ± 0.07 (where S????) between 1.4 and 17.9 GHz for the sample.
18192370
First results from the Very Small Array – IV. Cosmological parameter estimation
We investigate the constraints on basic cosmological parameters set by the first compact-configuration observations of the Very Small Array (VSA), and other cosmological data sets, in the standard inflationary ΛCDM model. Using the weak priors 40 < H0 < 90 km s−1 Mpc−1 and 0 < τ < 0.5, we find that the VSA and COBE-DMR data alone produce the constraints Ωtot= 1.03+0.12−0.12, Ωbh2= 0.029+0.009−0.009, Ωcdmh2= 0.13+0.08−0.05 and ns= 1.04+0.11−0.08 at the 68 per cent confidence level. Adding in the Type Ia supernova constraints, we additionally find Ωm= 0.32+0.09−0.06 and ΩΛ= 0.71+0.07−0.07. These constraints are consistent with those found by the BOOMERanG, DASI and MAXIMA experiments. We also find that, by combining all these cosmic microwave background experiments and assuming the Hubble Space Telescope Key Project limits for H0 (for which the X-ray plus Sunyaev–Zel'dovich route gives a similar result), we obtain the tight constraints Ωm= 0.28+0.14−0.07 and ΩΛ= 0.72+0.07−0.13, which are consistent with, but independent of, those obtained using the supernova data.
119201232
Sunyaev–Zel’dovich observation of the Bullet-like cluster Abell 2146 with the Arcminute Microkelvin Imager
We present 13.9―18.2 GHz observations of the Sunyaev-Zel'dovich (SZ) effect towards Abell 2146 using the Arcminute Microkelvin Imager (AMI). The cluster is detected with a peak signal-to-noise ratio of 13ϭ in the radio source subtracted map from 9 h of data. Comparison of the SZ image with the X-ray image from Russell et al. suggests that both have extended regions which lie approximately perpendicular to one another, with their emission peaks significantly displaced. These features indicate non-uniformities in the distributions of the gas temperature and pressure, and suggest complex dynamics indicative of a cluster merger. We use a fast, Bayesian cluster analysis to explore the high-dimensional parameter space of the cluster-plus-sources model to obtain robust cluster parameter estimates in the presence of radio point sources, receiver noise and primordial cosmic microwave background (CMB) anisotropy; despite the substantial radio emission from the direction of Abell 2146, the probability of SZ + CMB primordial structure + radio sources + receiver noise to CMB + radio sources + receiver noise is 3 x 10 6 : 1. We compare the results from three different cluster models. Our preferred model exploits the observation that the gas fractions do not appear to vary greatly between clusters. Given the relative masses of the two merging systems in Abell 2146, the mean gas temperature can be deduced from the virial theorem (assuming all of the kinetic energy is in the form of internal gas energy) without being affected significantly by the merger event, provided the primary cluster was virialized before the merger. In this model we fit a simple spherical isothermal β-model to our data, despite the inadequacy of this model for a merging system like Abell 2146, and assume the cluster follows the mass-temperature relation of a virialized, singular, isothermal sphere. We note that this model avoids inferring large-scale cluster parameters internal to r 200 under the widely used assumption of hydrostatic equilibrium. We find that at r 200 the average total mass M T = (4.1 ± 0.5) x 10 14 h ―1 M⊙ and the mean gas temperature T = 4.5 ± 0.5 keV.
59386633
Bayesian analysis of weak gravitational lensing and Sunyaev-Zel'dovich data for six galaxy clusters
We present an analysis of observations made with the Arcminute Microkelvin Imager (AMI) and the Canada–France–Hawaii Telescope (CFHT) of six galaxy clusters in a redshift range of 0.16–0.41. The cluster gas is modelled using the Sunyaev–Zel’dovich (SZ) data provided by AMI, while the total mass is modelled using the lensing data from the CFHT. In this paper, we (i) find very good agreement between SZ measurements (assuming large-scale virialization and a gas-fraction prior) and lensing measurements of the total cluster masses out to r200; (ii) perform the first multiple-component weak-lensing analysis of A115; (iii) confirm the unusual separation between the gas and mass components in A1914 and (iv) jointly analyse the SZ and lensing data for the relaxed cluster A611, confirming our use of a simulation-derived mass–temperature relation for parametrizing measurements of the SZ effect.