20 research outputs found
SuperCLASS - II. Photometric redshifts and characteristics of spatially resolved mu Jy radio sources
We present optical and near-infrared imaging covering a âŒ1.53âdeg2 region in the Super-Cluster Assisted Shear Survey (SuperCLASS) field, which aims to make the first robust weak lensing measurement at radio wavelengths. We derive photometric redshifts for â176â000 sources down to iâČABâŒ24 and present photometric redshifts for 1.4âGHz expanded Multi-Element Radio Linked Interferometer Network (e-MERLIN) and Karl G. Jansky Very Large Array (VLA) detected radio sources found in the central 0.26âdeg2. We compile an initial catalogue of 149 radio sources brighter than S1.4 > 75âÎŒJy and find their photometric redshifts span 0 7Ï in the density map and we confirm the photometric redshifts are consistent with previously measured spectra from a few galaxies at the cluster centres
SuperCLASS - III. Weak lensing from radio and optical observations in Data Release 1
We describe the first results on weak gravitational lensing from the SuperCLASS survey: the first survey specifically designed to measure the weak lensing effect in radio-wavelength data, both alone and in cross-correlation with optical data. We analyse 1.53deg2 of optical data from the Subaru telescope and 0.26deg2 of radio data from the e-MERLIN and VLA telescopes (the DR1 data set). Using standard methodologies on the optical data only we make a significant (10Ï) detection of the weak lensing signal (a shear power spectrum) due to the massive supercluster of galaxies in the targeted region. For the radio data we develop a new method to measure the shapes of galaxies from the interferometric data, and we construct a simulation pipeline to validate this method. We then apply this analysis to our radio observations, treating the e-MERLIN and VLA data independently. We achieve source densities of 0.5âarcminâ2 in the VLA data and 0.06âarcminâ2 in the e-MERLIN data, numbers which prove too small to allow a detection of a weak lensing signal in either the radio data alone or in cross-correlation with the optical data. Finally, we show preliminary results from a visibility-plane combination of the data from e-MERLIN and VLA which will be used for the forthcoming full SuperCLASS data release. This approach to data combination is expected to enhance both the number density of weak lensing sources available, and the fidelity with which their shapes can be measured
AMI-LA observations of the SuperCLASS supercluster
We present a deep survey of the SuperCLASS super-cluster - a region of sky
known to contain five Abell clusters at redshift - performed using
the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5GHz. Our
survey covers an area of approximately 0.9 square degrees. We achieve a nominal
sensitivity of Jy beam toward the field centre, finding 80
sources above a threshold. We derive the radio colour-colour
distribution for sources common to three surveys that cover the field and
identify three sources with strongly curved spectra - a high-frequency-peaked
source and two GHz-peaked-spectrum sources. The differential source count (i)
agrees well with previous deep radio source count, (ii) exhibits no evidence of
an emerging population of star-forming galaxies, down to a limit of 0.24mJy,
and (iii) disagrees with some models of the 15GHz source population.
However, our source count is in agreement with recent work that provides an
analytical correction to the source count from the SKADS Simulated Sky,
supporting the suggestion that this discrepancy is caused by an abundance of
flat-spectrum galaxy cores as-yet not included in source population models
SuperCLASS - I. The super cluster assisted shear survey: Project overview and data release 1
The SuperCLuster Assisted Shear Survey (SuperCLASS) is a legacy programme using the e-MERLIN interferometric array. The aim is to observe the sky at L-band (1.4âGHz) to a r.m.s. of 7ÎŒJybeamâ1 over an area of âŒ1deg2 centred on the Abell 981 supercluster. The main scientific objectives of the project are: (i) to detect the effects of weak lensing in the radio in preparation for similar measurements with the Square Kilometre Array (SKA); (ii) an extinction free census of star formation and AGN activity out to z ⌠1. In this paper we give an overview of the project including the science goals and multiwavelength coverage before presenting the first data release. We have analysed around 400âh of e-MERLIN data allowing us to create a Data Release 1 (DR1) mosaic of âŒ0.26deg2 to the full depth. These observations have been supplemented with complementary radio observations from the Karl G. Jansky Very Large Array (VLA) and optical/near infrared observations taken with the Subaru, Canada-France-Hawaii, and Spitzer Telescopes. The main data product is a catalogue of 887 sources detected by the VLA, of which 395 are detected by e-MERLIN and 197 of these are resolved. We have investigated the size, flux, and spectral index properties of these sources finding them compatible with previous studies. Preliminary photometric redshifts, and an assessment of galaxy shapes measured in the radio data, combined with a radio-optical cross-correlation technique probing cosmic shear in a supercluster environment, are presented in companion papers
The LOFAR Two-metre Sky Survey V. Second data release
In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey we present 120a 168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44 30a and 1h00m +28 00a and spanning 4178 and 1457 square degrees respectively. The images were derived from 3451 h (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4 396 228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6a resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 ΌJy beama 1; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2a; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy beama 1. By creating three 16 MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of > a ±a 0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20a resolution 120a168 MHz continuum images have a median rms sensitivity of 95 ΌJy beama 1, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480a A a 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy beama 1 at 4a and 2.2 mJy beama 1 at 20a; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data to facilitate the thorough scientific exploitation of this unique dataset
Deep observations of the super-CLASS supercluster at 325 MHz with the GMRT: The low-frequency source catalogue
SuperCLASS â II. Photometric redshifts and characteristics of spatially resolved ÎŒJy radio sources
The ultra-steep diffuse radio emission observed in the cool-core cluster RX J1720.1+2638 with LOFAR at 54Â MHz
Diffuse radio emission at the centre of galaxy clusters has been observed both in merging clusters on scales of Mpc, called giant radio haloes, and in relaxed systems with a cool-core on smaller scales, named mini haloes. Giant radio haloes and mini haloes are thought to be distinct classes of sources. However, recent observations have revealed the presence of diffuse radio emission on Mpc scales in clusters that do not show strong dynamical activity. RX J1720.1+2638 is a cool-core cluster, presenting both a bright central mini halo and a fainter diffuse, steep-spectrum emission extending beyond the cluster core that resembles giant radio halo emission. In this paper, we present new observations performed with the LOw Frequency ARray Low Band Antennas (LBA) at 54 MHz. These observations, combined with data at higher frequencies, allow us to constrain the spectral properties of the radio emission. The large-scale emission presents an ultrasteep spectrum with α14454âŒ3.2â . The radio emission inside and outside the cluster core have strictly different properties, as there is a net change in spectral index and they follow different radio-X-ray surface brightness correlations. We argue that the large-scale diffuse emission is generated by particles re-acceleration after a minor merger. While for the central mini halo, we suggest that it could be generated by secondary electrons and positrons from hadronic interactions of relativistic nuclei with the dense cool-core gas, as an alternative to re-acceleration models