119220088
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Perseus region
We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Serpens molecular cloud by the Spitzer c2d programme at a wavelength of 1.8 cm with the Arcminute Microkelvin Imager Large Array (AMI-LA). These observations have a resolution of ≈30 arcsec and an average sensitivity of 19µJy beam −1 .T he targets are predominantly Class I sources, and we find the detection rate for Class I objects in this sample to be low (18 per cent) compared to that of Class 0 objects (67 per cent), consistent with previous works. For detected objects we examine correlations of radio luminosity with bolometric luminosity and envelope mass and find that these data support correlations found by previous samples, but do not show any indication of the evolutionary divide hinted at by similar data from the Perseus molecular cloud when comparing radio luminosity with envelope mass. We conclude that envelope mass provides a better indicator for radio luminosity than bolometric luminosity, based on the distribution of deviations from the two correlations. Combining these new data with archival 3.6 cm flux densities we also examine the spectral indices of these objects and find an average spectral index of ¯ α 1.8 3.5 = 0.53 ± 1.14, consistent with the canonical value for a partially optically thick spherical or collimated stellar wind. However, we caution that possible inter-epoch variability limits the usefulness of this value, and such variability is supported by our identification of a possible flare in the radio history of Serpens SMM 1.
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.
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.
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.
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.
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.
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.
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.
43940631
Update on scalar singlet dark matter
One of the simplest models of dark matter is where a scalar singlet field S comprises some or all of the dark matter and interacts with the standard model through an vertical bar H vertical bar S-2(2) coupling to the Higgs boson. We update the present limits on the model from LHC searches for invisible Higgs decays, the thermal relic density of S, and dark matter searches via indirect and direct detection. We point out that the currently allowed parameter space is on the verge of being significantly reduced with the next generation of experiments. We discuss the impact of such constraints on possible applications of scalar singlet dark matter, including a strong electroweak phase transition, and the question of vacuum stability of the Higgs potential at high scales.
122558225
Gamma-Rays from Ultracompact Primordial Dark Matter Minihalos
Ultracompact minihalos have been proposed as a new class of dark matter structure. They would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute nonbaryonic massive compact halo objects today. We examine the prospects of detecting these minihalos in gamma rays if dark matter can self-annihilate. We compute present-day fluxes from minihalos produced in the e(+)e(-) annihilation epoch and the QCD and electroweak phase transitions. Even at a distance of 4 kpc, minihalos from the e(+)e(-) epoch would be eminently detectable today by the Fermi satellite or air Ccerenkov telescopes, or even in archival EGRET data. Within 2 kpc, they would appear as extended sources to Fermi. At 4 kpc, minihalos from the QCD transition have similar predicted fluxes to dwarf spheroidal galaxies, so might also be detectable by present or upcoming experiments.