We have obtained deep Sunyaev-Zel'dovich (SZ) observations towards 15 of the hottest XMM Cluster Survey (XCS) clusters that can be observed with the Arcminute Microkelvin Imager (AMI). We use a ...Bayesian analysis to quantify the significance of our SZ detections. We detect the SZ effect at high significance towards three of the clusters and at lower significance for a further two clusters. Towards the remaining 10 clusters, no clear SZ signal was measured. We derive cluster parameters using the XCS mass estimates as a prior in our Bayesian analysis. For all AMI-detected clusters, we calculate large-scale mass and temperature estimates while for all undetected clusters we determine upper limits on these parameters. We find that the large-scale mean temperatures derived from our AMI SZ measurements (and the upper limits from null detections) are substantially lower than the XCS-based core-temperature estimates. For clusters detected in the SZ, the mean temperature is, on average, a factor of 1.4 lower than temperatures from the XCS. Our upper limits on the cluster temperature of undetected systems are lower than the mean XCS derived temperature.
ABSTRACT We present 13.9-18.2GHz observations of the Sunyaev-Zel'dovich (SZ) effect towards Abell2146 using the Arcminute Microkelvin Imager (AMI). The cluster is detected with a peak signal-to-noise ...ratio of 13σ in the radio source subtracted map from 9h 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 Abell2146, the probability of SZ + CMB primordial structure + radio sources + receiver noise to CMB + radio sources + receiver noise is 3 × 106:1. 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 Abell2146, 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 Abell2146, 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 r200 under the widely used assumption of hydrostatic equilibrium. We find that at r200 the average total mass MT= (4.1 ± 0.5) × 1014h-1M and the mean gas temperature T= 4.5 ± 0.5keV. PUBLICATION ABSTRACT
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We present deep 1.8 cm (16 GHz) radio continuum imaging of seven young stellar objects in the Taurus molecular cloud. These objects have previously been extensively studied in the submm to ...near-infrared range and their spectral energy distributions modelled to provide reliable physical and geometrical parameters. We use these new data to constrain the properties of the long-wavelength tail of the greybody spectrum, which is expected to be dominated by emission from large dust grains in the protostellar disc. We find spectra consistent with the opacity indices expected for such a population, with an average opacity index of β= 0.26 ± 0.22 indicating grain growth within the discs. We use spectra fitted jointly to radio and submm data to separate the contributions from thermal dust and radio emission at 1.8 cm and derive disc masses directly from the cm-wave dust contribution. We find that disc masses derived from these flux densities under assumptions consistent with the literature are systematically higher than those calculated from submm data, and meet the criteria for giant planet formation in a number of cases.
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 r
200; (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.
We present follow-up observations of 97 point sources from the Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr data, contained within the New Extragalactic WMAP Point Source catalogue between −4°≤δ≤ ...60°; the sources form a flux-density-limited sample complete to 1.1 Jy (≈5σ) at 33 GHz. Our observations were made at 16 GHz using the Arcminute Microkelvin Imager and at 33 GHz with the Very Small Array (VSA). 94 of the sources have reliable, simultaneous – typically a few minutes apart – observations with both telescopes. The spectra between 13.9 and 33.75 GHz are very different from those of bright sources at low frequency: 44 per cent have rising spectra (α33.7513.9 < 0.0), where S∝ν−α, and 93 per cent have spectra with α33.7513.9 < 0.5; the median spectral index is 0.04. For the brighter sources, the agreement between VSA and WMAP 33-GHz flux densities averaged over sources is very good. However, for the fainter sources, the VSA tends to measure lower values for the flux densities than WMAP. We suggest that the main cause of this effect is the Eddington bias arising from variability.
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 13σ 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 × 106 : 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) × 1014
h
−1 M⊙ and the mean gas temperature T= 4.5 ± 0.5 keV.
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, r
200 being the virial radius. Reaching r
200 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.
We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Perseus molecular cloud by the Spitzer c2d programme at a wavelength of 1.8 cm ...with the Arcminute Microkelvin Imager Large Array (AMI-LA). We detect 72 per cent of Class 0 objects from this sample and 31 per cent of Class I objects. No starless cores are detected. We use the flux densities measured from these data to improve constraints on the correlations between radio luminosity and bolometric luminosity, infrared luminosity and, where measured, outflow force. We discuss the differing behaviour of these objects as a function of protostellar class and investigate the differences in radio emission as a function of core mass. Two of four possible very low luminosity objects (VeLLOs) are detected at 1.8 cm.
Most Sunyaev-Zel'dovich (SZ) and X-ray analyses of galaxy clusters try to constrain the cluster total mass (M
T(r)) and/or gas mass (M
g(r)) using parametrized models derived from both simulations ...and imaging observations, and assumptions of spherical symmetry and hydrostatic equilibrium. By numerically exploring the probability distributions of the cluster parameters given the simulated interferometric SZ data in the context of Bayesian methods, and assuming a β-model for the electron number density n
e(r) described by two shape parameters β and r
c, we investigate the capability of this model and analysis to return the simulated cluster input quantities via three parametrizations. In parametrization I we assume that the gas temperature is an independent free parameter and assume hydrostatic equilibrium, spherical geometry and an ideal gas equation of state. We find that parametrization I can hardly constrain the cluster parameters and fails to recover the true values of the simulated cluster. In particular it overestimates M
T(r
200) and T
g(r
200) (M
T(r
200) = (6.43 ± 5.43) × 1015 M⊙ and T
g(r
200) = (10.61 ± 5.28) keV) compared to the corresponding values of the simulated cluster (M
T(r
200) = 5.83 × 1014 M⊙ and T
g(r
200) = 5 keV). We then investigate parametrizations II and III in which f
g(r
200) replaces temperature as a main variable; we do this because f
g may vary significantly less from cluster to cluster than temperature. In parametrization II we relate M
T(r
200) and T
g assuming hydrostatic equilibrium. We find that parametrization II can constrain the cluster physical parameters but the temperature estimate is biased low (M
T(r
200) = (6.8 ± 2.1) × 1014 M⊙ and T
g(r
200) = (3.0 ± 1.2) keV). In parametrization III, the virial theorem (plus the assumption that all the kinetic energy of the cluster is the internal energy of the gas) replaces the hydrostatic equilibrium assumption because we consider it more robust both in theory and in practice. We find that parametrization III results in unbiased estimates of the cluster properties (M
T(r
200) = (4.68 ± 1.56) × 1014 M⊙ and T
g(r
200) = (4.3 ± 0.9) keV). We generate a second simulated cluster using a generalized Navarro-Frenk-White pressure profile and analyse it with an entropy-based model to take into account the temperature gradient in our analysis and improve the cluster gas density distribution. This model also constrains the cluster physical parameters and the results show a radial decline in the gas temperature as expected. The mean cluster total mass estimates are also within 1σ from the simulated cluster true values: M
T(r
200) = (5.9 ± 3.4) × 1014 M⊙ and T
g(r
200) = (7.4 ± 2.6) keV using parametrization II, and M
T(r
200) = (8.0 ± 5.6) × 1014 M⊙ and T
g(r
200) = (5.98 ± 2.43) keV using parametrization III. However, we find that for at least interferometric SZ analysis in practice at the present time, there is no differences in the Arcminute Microkelvin Imager (AMI) visibilities between the two models. This may of course change as the instruments improve.
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