Search

We present optical and near-infrared imaging covering a $\sim$1.53 deg$^2$ 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 $\approx$176,000 sources down to $i^\prime_{\rm AB}\sim24$ and present photometric redshifts for 1.4 GHz $e$-MERLIN and VLA detected radio sources found in the central 0.26 deg$^{2}$. We compile an initial catalog of 149 radio sources brighter than S$_{1.4}>75$ $��$Jy and find their photometric redshifts span $07 ��$ in the density map and we confirm the photometric redshifts are consistent with previously measured spectra from a few galaxies at the cluster centers., 14 pages, 13 figures, accepted for publication in MNRAS on March 3 2020

The Karl G. Jansky Very Large Array (VLA) is currently the world's most powerful cm-wavelength telescope. However, within a few years this blanket statement will no longer be entirely true, due to the emergence of a new breed of pre-SKA radio telescopes with improved surveying capabilities. This white paper explores a region of sensitivity-area parameter space where an investment of a few thousand hours through a VLA Sky Survey (VLASS) will yield a unique dataset with extensive scientific utility and legacy value well into the SKA era: a deep full-polarization L-band survey covering a few square degrees in A-configuration. Science that can be addressed with a deep VLASS includes galaxy evolution, dark energy and dark matter using radio weak lensing, and cosmic magnetism. A deep VLASS performed in a field with extensive multiwavelength data would also deliver a gold standard multiwavelength catalog to inform wider and shallower surveys such as SKA1-survey., Comment: 9 pages, 5 figures, comments welcome

We present BLOBCAT, new source extraction software that utilises the flood fill algorithm to detect and catalogue blobs, or islands of pixels representing sources, in two-dimensional astronomical images. The software is designed to process radio-wavelength images of both Stokes I intensity and linear polarization, the latter formed through the quadrature sum of Stokes Q and U intensities or as a byproduct of rotation measure synthesis. We discuss an objective, automated method by which estimates of position-dependent background root-mean-square noise may be obtained and incorporated into BLOBCAT's analysis. We derive and implement within BLOBCAT corrections for two systematic biases to enable the flood fill algorithm to accurately measure flux densities for Gaussian sources. We discuss the treatment of non-Gaussian sources in light of these corrections. We perform simulations to validate the flux density and positional measurement performance of BLOBCAT, and we benchmark the results against those of a standard Gaussian fitting task. We demonstrate that BLOBCAT exhibits accurate measurement performance in total intensity and, in particular, linear polarization. BLOBCAT is particularly suited to the analysis of large survey data. The BLOBCAT software, supplemented with test data to illustrate its use, is available at: http://blobcat.sourceforge.net/ ., Comment: 19 pages, 13 figures, accepted for publication in MNRAS

Context. The Australia Telescope Large Area Survey (ATLAS) aims to image a 7 deg2 region centred on the European Large Area ISO Survey - South 1 (ELAIS-S1) field and the Chandra Deep Field South (CDF-S) at 1.4 GHz with high sensitivity (up to ~10 \muJy) to study the evolution of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) over a wide range of cosmic time. Aims. We present here ancillary radio observations at a frequency of 2.3 GHz obtained with the Australia Telescope Compact Array (ATCA). The main goal of this is to study the radio spectra of an unprecedented large sample of sources (~2000 observed, ~600 detected in both frequencies). Methods. With this paper, we provide 2.3 GHz source catalogues for both ATLAS fields, with a detection limit of 300 \muJy. We compute spectral indices between 1.4 GHz and 2.3 GHz using matched resolution images and investigate various properties of our source sample in dependence of their spectral indices. Results. We find the entire source sample to have a median spectral index of 0.74, in good agreement with both the canonical value of 0.7 for optically thin synchrotron radiation and other spectral index studies conducted by various groups. Regarding the radio spectral index as indicator for source type, we find only marginal correlations so that flat or inverted spectrum sources are usually powered by AGN and hence conclude that at least for the faint population the spectral index is not a strong discriminator. We investigate relation between spectral index and redshift for our source sample and find no such correlation at all. We do find a significant correlation between redshift and radio to near-infrared flux ratio, making this a much stronger tracer of high-z radio sources. We also find no evidence for a dependence of the radio-IR correlation on spectral index., Comment: 12 pages, 13 figures, accepted for publication by A&A, Table 2 will be available electronically once published

A fully analytic statistical formalism does not yet exist to describe radio-wavelength measurements of linearly polarized intensity that are produced using rotation measure synthesis. In this work we extend the analytic formalism for standard linear polarization, namely that describing measurements of the quadrature sum of Stokes Q and U intensities, to the rotation measure synthesis environment. We derive the probability density function and expectation value for Faraday-space polarization measurements for both the case where true underlying polarized emission is present within unresolved Faraday components, and for the limiting case where no such emission is present. We then derive relationships to quantify the statistical significance of linear polarization measurements in terms of standard Gaussian statistics. The formalism developed in this work will be useful for setting signal-to-noise ratio detection thresholds for measurements of linear polarization, for the analysis of polarized sources potentially exhibiting multiple Faraday components, and for the development of polarization debiasing schemes., Comment: 14 pages, 6 figures, accepted for publication in MNRAS

The Next-Generation Very Large Array (ngVLA) will be critical for understanding how galaxies are built and evolve at the earliest epochs. The sensitivity and frequency coverage will allow for the detection of cold gas and dust in `normal' distant galaxies, including the low-J transitions of molecular gas tracers such as CO, HNC, and HCO+; synchrotron and free-free continuum emission; and even the exciting possibility of thermal dust emission at the highest (z~7) redshifts. In particular, by enabling the total molecular gas reservoirs to be traced to unprecedented sensitivities across a huge range of epochs simultaneously -- something no other radio or submillimeter facility will be capable of -- the detection of the crucial low-J transitions of CO in a diverse body of galaxies will be the cornerstone of ngVLA's contribution to high-redshift galaxy evolution science. The ultra-wide bandwidths will allow a complete sampling of radio SEDs, as well as the detection of emission lines necessary for spectroscopic confirmation of elusive dusty starbursts. The ngVLA will also deliver unique contributions to our understanding of cosmic magnetism and to science accessible through microwave polarimetry. Finally, the superb angular resolution will move the field beyond detection experiments and allow detailed studies of the morphology and dynamics of these systems, including dynamical modeling of disks/mergers, determining the properties of outflows, measuring black hole masses from gas disks, and resolving multiple AGN nuclei. We explore the contribution of a ngVLA to these areas and more, as well as synergies with current and upcoming facilities including ALMA, SKA, large single-dish submillimeter observatories, GMT/TMT, and JWST., Comment: 52 pages, 13 figures, NRAO Next Generation Very Large Array Memos Series: http://library.nrao.edu/ngvla.shtml