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 deg2 of the Galactic plane, covering the area 76°
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.
Abstract
Arcminute Microkelvin Imager observations towards CIZA J2242+5301, in comparison with observations of weak gravitational lensing and X-ray emission from the literature, are used to ...investigate the behaviour of non-baryonic dark matter (NBDM) and gas during the merger. Analysis of the Sunyaev–Zel'dovich (SZ) signal indicates the presence of high pressure gas elongated perpendicularly to the X-ray and weak-lensing morphologies, which, given the merger-axis constraints in the literature, implies that high pressure gas is pushed out into a linear structure during core passing. Simulations in the literature closely matching the inferred merger scenario show the formation of gas density and temperature structures perpendicular to the merger axis. These SZ observations are challenging for modified gravity theories in which NBDM is not the dominant contributor to galaxy-cluster gravity.
We observed the cluster CIZA J2242.8+5301 with the Arcminute Microkelvin Imager at 16 GHz and present the first high radio-frequency detection of diffuse, non-thermal cluster emission. This cluster ...hosts a variety of bright, extended, steep-spectrum synchrotron-emitting radio sources, associated with the intracluster medium, called radio relics. Most notably, the northern, Mpc-wide, narrow relic provides strong evidence for diffusive shock acceleration in clusters. We detect a puzzling, flat-spectrum, diffuse extension of the southern relic, which is not visible in the lower radio-frequency maps. The northern radio relic is unequivocally detected and measures an integrated flux of 1.2 ± 0.3 mJy. While the low-frequency (<2 GHz) spectrum of the northern relic is well represented by a power law, it clearly steepens towards 16 GHz. This result is inconsistent with diffusive shock acceleration predictions of ageing plasma behind a uniform shock front. The steepening could be caused by an inhomogeneous medium with temperature/density gradients or by lower acceleration efficiencies of high energy electrons. Further modelling is necessary to explain the observed spectrum.
Using Arcminute Microkelvin Imager (AMI) Sunyaev–Zel'dovich (SZ) observations towards 10 CLASH (Cluster Lensing and Supernova Survey with Hubble) clusters, we investigate the influence of cluster ...mergers on observational galaxy cluster studies. Although selected to be largely relaxed, there is disagreement in the literature on the dynamical states of CLASH sample members. We analyse our AMI data in a fully Bayesian way to produce estimated cluster parameters and consider the intrinsic correlations in our Navarro, Frenk and White/generalized Navarro, Frenk and White-based model. Varying pressure profile shape parameters, illustrating an influence of mergers on scaling relations, induces small deviations from the canonical self-similar predictions – in agreement with simulations of Poole et al. (2007) who found that merger activity causes only small scatter perpendicular to the relations. We demonstrate this effect observationally using the different dependences of SZ and X-ray signals to n
e that cause different sensitivities to the shocking and/or fractionation produced by mergers. Plotting Y
X–M
gas relations (where Y
X = M
gas
T) derived from AMI SZ and from Chandra X-ray gives ratios of AMI and Chandra
Y
X and M
gas estimates that indicate movement of clusters along the scaling relation, as predicted by Poole et al. (2007). Clusters that have moved most along the relation have the most discrepant T
SZ and T
X estimates: all the other clusters (apart from one) have SZ and X-ray estimates of M
gas, T and Y
X that agree within r
500. We use SZ versus X-ray discrepancies in conjunction with Chandra maps and T
X profiles, making comparisons with simulated cluster merger maps in Poole et al. (2006) to identify disturbed members of our sample and estimate merger stages.
We present 16-GHz Sunyaev-Zel'dovich observations using the Arcminute Microkelvin Imager (AMI) and subsequent Bayesian analysis of six galaxy clusters at redshift z 1 chosen from an X-ray- and ...infrared-selected sample from Culverhouse et al. In the subsequent analysis, we use two cluster models, an isothermal β-model and a Dark Matter Generalised Navarro-Frenk-White (DM-GNFW) model in order to derive a formal detection probability and the cluster parameters. We detect two clusters (CL J1415+3612 and XMJ 0830+5241) and measure their total masses out to a radius of 200 times the critical density at the respective cluster's redshift. For CL J1415+3612, we find M
T, 200 = 7.3
× 1014 M (β-model) and M
T, 200 = 10.42.5
− 2.4 × 1014 M (DM-GNFW model) and for XMJ0830+5241, we find M
T, 200 = 3.6
× 1014 M, (β-model) and M
T, 200 = 4.7
× 1014 M (DM-GNFW model), which agree with each other for each cluster. We also present maps before and after source subtraction of the entire sample and provide 1D and 2D posterior marginalized probability distributions for each fitted cluster profile parameter of the detected clusters. Using simulations which take into account the measured source environment from the AMI Large Array (LA), source confusion noise, cosmic microwave background primordials, instrument noise, we estimate from small-radius (r
2500) X-ray data from Culverhouse et al., the detectability of each cluster in the sample and compare it with the result from the Small Array (SA) data. Furthermore, we discuss the validity of the assumptions of isothermality and constant gas mass fraction. We comment on the bias that these small-radius estimates introduce to large-radius SZ predictions. In addition, we follow-up the two detections with deep, single-pointed LA observations. We find a 3σ tentative decrement towards CL J1415+3612 at high resolution and a 5σ high-resolution decrement towards XM J0830+5241.
In a previous paper (Paper I), the observational, mapping and source-extraction techniques used for the Tenth Cambridge (10C) Survey of Radio Sources were described. Here, the first results from the ...survey, carried out using the Arcminute Microkelvin Imager Large Array (LA) at an observing frequency of 15.7 GHz, are presented. The survey fields cover an area of ≈27 deg2 to a flux-density completeness of 1 mJy. Results for some deeper areas, covering ≈12 deg2, wholly contained within the total areas and complete to 0.5 mJy, are also presented. The completeness for both areas is estimated to be at least 93 per cent. The 10C survey is the deepest radio survey of any significant extent (≳0.2 deg2) above 1.4 GHz.
The 10C source catalogue contains 1897 entries and is available online. The source catalogue has been combined with that of the Ninth Cambridge Survey to calculate the 15.7-GHz source counts. A broken power law is found to provide a good parametrization of the differential count between 0.5 mJy and 1 Jy. The measured source count has been compared with that predicted by de Zotti et al. - the model is found to display good agreement with the data at the highest flux densities. However, over the entire flux-density range of the measured count (0.5 mJy to 1 Jy), the model is found to underpredict the integrated count by ≈30 per cent.
Entries from the source catalogue have been matched with those contained in the catalogues of the NRAO VLA Sky Survey and the Faint Images of the Radio Sky at Twenty-cm survey (both of which have observing frequencies of 1.4 GHz). This matching provides evidence for a shift in the typical 1.4-GHz spectral index to 15.7-GHz spectral index of the 15.7-GHz-selected source population with decreasing flux density towards sub-mJy levels - the spectra tend to become less steep.
Automated methods for detecting extended sources, developed in Paper I, have been applied to the data; ≈5 per cent of the sources are found to be extended relative to the LA-synthesized beam of ≈30 arcsec. Investigations using higher resolution data showed that most of the genuinely extended sources at 15.7 GHz are classical doubles, although some nearby galaxies and twin-jet sources were also identified.
ABSTRACT We have observed an area of asymptotically =27deg2 to an rms noise level of 0.2mJy at 15.7 GHz, using the Arcminute Microkelvin Imager Large Array. These observations constitute the most ...sensitive radio-source survey of any extent (0.2deg2) above 1.4 GHz. This paper presents the techniques employed for observing, mapping and source extraction. We have used a systematic procedure for extracting information and producing source catalogues, from maps with varying noise anduv-coverage. We have performed simulations to test our mapping and source-extraction procedures, and developed methods for identifying extended, overlapping and spurious sources in noisy images. In an accompanying paper, AMI Consortium: Davies et al., the first results from the 10C survey, including the deep 15.7-GHz source count, are presented. PUBLICATION ABSTRACT
We present Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of a massive galaxy cluster discovered in the Arcminute Microkelvin Imager (AMI) blind Sunyaev-Zel'dovich (SZ) ...survey. Without knowledge of the cluster redshift a Bayesian analysis of the AMI, CARMA and joint AMI and CARMA uv-data is used to quantify the detection significance and parametrize both the physical and observational properties of the cluster whilst accounting for the statistics of primary cosmic microwave background anisotropies, receiver noise and radio sources. The joint analysis of the AMI and CARMA uv-data was performed with two parametric physical cluster models: the β-model; and the model described in Olamaie et al. with the pressure profile fixed according to Arnaud et al. The cluster mass derived from these different models is comparable but our Bayesian evidences indicate a preference for the β-profile which we, therefore, use throughout our analysis. From the CARMA data alone we obtain a formal Bayesian probability of detection ratio of 12.8:1 when assuming that a cluster exists within our search area; alternatively assuming that Jenkins et al. accurately predict the number of clusters as a function of mass and redshift, the formal Bayesian probability of detection is 0.29:1. From the Bayesian analysis of the AMI or AMI and CARMA data the probability of detection ratio exceeds 4.5 × 103:1. Performing a joint analysis of the AMI and CARMA data with a physical cluster model we derive the total mass internal to r
200 as M
T, 200 = 4.1 ± 1.1 × 1014 M. Using a phenomenological β-model to quantify the temperature decrement as a function of angular distance we find a central SZ temperature decrement of 170 ± 24 μK in the AMI and CARMA data. The SZ decrement in the CARMA data is weaker than expected and we speculate that this is a consequence of the cluster morphology. In a forthcoming study the pipeline that we have developed for the analyses of these data will be used to thoroughly assess the impact of cluster morphology on the SZ decrements that are observed with interferometers such as AMI and CARMA.
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.
We present 16 GHz (1.9 cm) deep radio continuum observations made with the Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets. We combine these new data with archival ...information from an extensive literature search to examine spectral energy distributions (SEDs) for each source and calculate both the radio and sub-mm spectral indices in two different scenarios: (1) fixing the dust temperature (T
d) according to evolutionary class; and (2) allowing T
d to vary. We use the results of this analysis to place constraints on the physical mechanisms responsible for the radio emission. From AMI data alone, as well as from model fitting to the full SED in both scenarios, we find that 80 per cent of the objects in this sample have spectral indices consistent with free-free emission. We find an average spectral index in both T
d scenarios, consistent with free-free emission. We examine correlations of the radio luminosity with bolometric luminosity, envelope mass and outflow force, and find that these data are consistent with the strong correlation with envelope mass seen in lower luminosity samples. We examine the errors associated with determining the radio luminosity and find that the dominant source of error is the uncertainty on the opacity index, β. We examine the SEDs for variability in these young objects, and find evidence for possible radio flare events in the histories of L1551 IRS 5 and Serpens SMM 1.
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