28 research outputs found
28 -- 40 GHz variability and polarimetry of bright compact sources in the QUIJOTE cosmological fields
We observed 51 sources in the Q-U-I JOint TEnerife (QUIJOTE) cosmological
fields which were brighter than 1 Jy at 30 GHz in the Planck Point Source
Catalogue (version 1), with the Very Large Array at 28 -- 40 GHz, in order to
characterise their high-radio-frequency variability and polarization
properties. We find a roughly log-normal distribution of polarization fractions
with a median of 2%, in agreement with previous studies, and a median rotation
measure (RM) of 1110 rad m with one outlier up to
64000 rad m which is among the highest RMs measured in quasar cores. We
find hints of a correlation between the total intensity flux density and median
polarization fraction. We find 59% of sources are variable in total intensity,
and 100% in polarization at level, with no apparent correlation
between total intensity variability and polarization variability. This
indicates that it will be difficult to model these sources without simultaneous
polarimetric monitoring observations and they will need to be masked for
cosmological analysis.Comment: 17 pages, 14 figures, accepted to MNRA
The highest frequency detection of a radio relic : 16 GHz AMI observations of the 'Sausage' cluster
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters. © 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.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.Peer reviewe
Physical modelling of galaxy clusters detected by the Planck satellite
We present a comparison of mass estimates for galaxy cluster candidates from the second Planck catalogue (PSZ2) of Sunyaev-Zel'dovich sources. We compare the mass values obtained with data taken from the Arcminute Microkelvin Imager (AMI) radio interferometer system and from the Planck satellite. The former of these uses a Bayesian analysis pipeline that parameterises a cluster in terms of its physical quantities, and models the dark matter & baryonic components of a cluster using NFW and GNFW profiles respectively. Our mass estimates derived from Planck data are obtained from the results of the Bayesian detection algorithm PowellSnakes (PwS), are based on the methodology detailed in the PSZ2 paper, and produce two sets of mass estimates; one estimate is calculated directly from the angular radius - integrated Comptonisation parameter posterior distributions, and the other uses a `slicing function' to provide information on based on X-ray measurements and previous Planck mission samples. We find that for of the clusters, the AMI mass estimates are lower than both values obtained from Planck data. However the AMI and slicing function estimates are within one combined standard deviation of each other for clusters. We also generate cluster simulations based on the slicing-function mass estimates, and analyse them in the same way as we did the real AMI data. We find that inclusion in the simulations of radio-source confusion & CMB noise and measurable radio-sources causes AMI mass estimates to be systematically low.This work was performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing (HPC) Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council ..â . Kamran Javid acknowledges an STFC studentship. Yvette Perrott acknowledges support from a Trinity College Junior Research Fellowship
AMI observations of unmatched Planck ERCSC LFI sources at 15.75 GHz
The Planck Early Release Compact Source Catalogue includes 26 sources with no
obvious matches in other radio catalogues (of primarily extragalactic sources).
Here we present observations made with the Arcminute Microkelvin Imager Small
Array (AMI SA) at 15.75 GHz of the eight of the unmatched sources at
declination > +10 degrees. Of the eight, four are detected and are associated
with known objects. The other four are not detected with the AMI SA, and are
thought to be spurious.Comment: 6 pages, 5 figures, 4 table
A joint analysis of AMI and CARMA observations of the recently discovered SZ galaxy cluster system AMI-CL J0300+2613
Saunder
Radio continuum observations of Class I protostellar disks in Taurus: constraining the greybody tail at centimetre wavelengths
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 sub-mm to NIR range and their SEDs modelled to
provide reliable physical and geometrical parametres.We use this 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 disk. We find spectra consistent with the opacity indices expected
for such a population, with an average opacity index of beta = 0.26+/-0.22
indicating grain growth within the disks. We use spectra fitted jointly to
radio and sub-mm data to separate the contributions from thermal dust and radio
emission at 1.8 cm and derive disk masses directly from the cm-wave dust
contribution. We find that disk masses derived from these flux densities under
assumptions consistent with the literature are systematically higher than those
calculated from sub-mm data, and meet the criteria for giant planet formation
in a number of cases.Comment: submitted MNRA
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 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% of Class 0 objects from this sample
and 31% 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.Comment: 18 pages, 9 figures, accepted MNRA