Name

Sanjay Bhatnagar

Wide-band wide-field full-polarization imaging: Challenges, progress and plans

All modern radio interferometric telescopes have sensitivities in access of 10x better and use wider bandwidth receivers compared to previous generation telescopes. The telescope sensitivity pattern therefore covers a significantly larger region on the sky. Many also operate at relatively lower frequencies where the sky is brighter and more filled with emission. Noise limited imaging with such telescopes therefore necessarily require wide-band wide-field imaging. Furthermore, at these high sensitivities, in-beam effects, in particular off-axis direction-dependent polarization effects also need to be corrected during imaging. Wide-field wide-band full-polarization imaging is therefore a requirement with these telescopes and not an exception as with previous generation telescopes. Significant progress via development of new wide-band imaging and image reconstruction algorithms has been made in recent years. This has enabled wide-field imaging with many low-frequency telescopes. In this talk, I will give an over view of the on-going research and development with a focus on accounting for off-axis polarization effects to enable wide-field full-polarization imaging capabilities. Since the data volumes from modern telescopes in the Tera bytes range and the new algorithms also require significantly higher computing, I will also discuss the high performance computing problem posed by wide-field wide-band full-polarization imaging, the solutions being pursued and the current status via some results.

Paolo Ciliegi

The ATCA- CABB survey in the XXL field

The XXL survey comprises the largest XMM-Newton project approved to date. The main goals of this X-ray survey are to provide long-lasting legacy data for studies of galaxy clusters and AGN. To provide the complementary radio data, a large survey with the ATCA-CABB array has been obtained down to an average rms of 50 microJy. This will allow us detailed studies of the role of radio mode feedback on the formation and evolution of galaxies and galaxy cluster. In this talk I will present the results of the XXL radio survey (source counts, spectral index) and the optical/NIR identification of the radio sources obtained with the Likelihood Ratio technique. The optimized procedures for the radio-optical associations can be an useful tool for the optical identification of the radio sources detected in the SPARCS surveys.

Chiara Ferrari

Multi-frequency image reconstruction for radio interferometry. A regularized inverse problem approach

Authors: André Ferrari, Jérémy Deguignet, Chiara Ferrari, David Mary, Antony Schutz, Oleg Smirnov We describe a ``spatio-spectral'' deconvolution algorithm for wide-band imaging in radio interferometry. In contrast with the existing multi-frequency reconstruction algorithms, the proposed method does not rely on a model of the sky-brightness spectral distribution. This non-parametric approach can be of particular interest for the new generation of low frequency radiotelescopes. The proposed solution formalizes the reconstruction problem as a convex optimization problem with spatial and spectral regularizations. The efficiency of this approach has been already proven for narrow-band image reconstruction and the present contribution can be considered as its extension to the multi-frequency case. Because the number of frequency bands multiplies the size of the inverse problem, particular attention is devoted to the derivation of an iterative large scale optimization algorithm. It is shown that the main computational bottleneck of the approach, which lies in the resolution of a linear system, can be efficiently overcome by a fully parallel implementation w.r.t. the frequencies, where each processor reconstructs a narrow-band image. All the other optimization steps are extremely fast. A parallel implementation of the algorithm in Julia is publicly available at https://github.com/andferrari. Preliminary simulations illustrate the performances of the method and its ability to reconstruct complex spatio-spectral structures.

Tony Foley and Nadeem Ozeer

KISS: The KAT-7 Interferometric Sky Survey

The KISS survey has been started to get some practical experience in data flow and pipelining for the automated surveys in the future. Some results will be presented and a discussion of the automated flagging and pipeline of this data will be done. We would also like to discuss concepts for an early science MeerKAT survey. This could serve as a test-bed for the software tools which will be needed when MeerKAT is available for the large survey proposals. In particular what are the most efficient flagging systems, the optimal source finders and how to manage large catalogues that will be generated when making an initial (partial) sky model that will be needed for later for the deep surveys.

Ian Heywood

Wide field, wide band continuum imaging with ASKAP BETA

The Boolardy Engineering Test Array (BETA) is the six antenna prototype of the Australian Square Kilometre Array Pathfinder. Equipped with Mk1 Phased Array Feeds, it is presently capable of delivering nine independent formed beams that can be placed arbitrarily within its ~30 square degree field of view, each recording 300 MHz of bandwidth. I will present an overview of one of the commissioning projects, namely a pilot 150 sq. deg. continuum survey at 711 - 1015 MHz that reaches sub-mJy depths in a single 12 hour run. These observations have been used for astrometric, photometric and spectroscopic verification, in addition to optimising methods for fully automated pipelining. We have observed the field on three separate dates, thus in addition to testing the stability of the system the project also serves as a pilot variability survey.

Ian Heywood

Lessons learnt from a pair of VLA continuum surveys at 1-2 GHz

Data for two complementary continuum surveys have been recorded using the Karl G. Jansky Very Large Array at 1-2 GHz. The first is a snapshot survey of SDSS Stripe 82 in the hybrid CnB configuration, consisting of 1,027 x 2.5 minute pointings with a final coverage of ~72 sq. deg. The second is a deeper, narrower survey of the XMM-LSS / VIDEO field, consisting of 32 x 1 hour pointings, covering 4.5 sq. deg using the B-configuration. I will present the products of these surveys, discuss the pitfalls encountered during calibration and imaging and comment on how these findings are applicable to the next generation of radio continuum surveys.

Minh Huynh

ATCA 2.1GHz Observations of the XXL-S Field: Survey Description and Initial Results

The XXL is the largest survey ever with the XMM-Newton telescope, comprising 6.9 MS spread over two 25 sq deg fields, the XMM-LSS field (XXL-N RA=2:18, Dec=-5:17) and the BCS-XMM field (XXL-S at RA=23:30, Dec=-54:30). The main goals of the XXL project are to probe cosmology using galaxy clusters and to study galaxy evolution with a large sample of AGN. As part of the ongoing multiwavelength followup to achieve these science goals, a pilot survey was performed on the Australia Telescope Compact Array to cover the central 5 sq deg of XXL-S at 2.1 GHz, achieving an sensitivity of ~50 microJy rms. We observed the remaining 20 sq deg of the XXL-S in late 2014. Here we present the full ATCA 2.1 GHz image of the full 25 sq deg of the XXL-S, which has an rms noise of ~35--50 microJy and a resolution of ~5 arcsec. This is the largest radio survey ever at these flux density levels. We identify ~7000 radio sources down to 5 sigma.

Preshanth Jagannathan

Off-Axis Direction Dependent Polarization Effects, Corrections and Imaging Limits.

High fidelity and high dynamic range continuum imaging is required for the various science drivers of the next generation of radio telescopes. Noise limited imaging with modern high-sensitivity wide bandwidth telescopes requires correction of various direction dependent effects, including off-axis in-beam polarization effects during imaging, in addition to frequency and temporal variation of the antenna sensitivity pattern. In this talk I will discuss the use WBA-Projection for correcting the direction dependent primary beam effects in full polarization. I will further discuss the imaging limits at which these advanced imaging algorithms are indispensable and highlight the need for wide band direction dependent imaging to be able to carryout wide field full polarimetric surveys.

Sthabile Kolwa

The Effect of Environment on Black-Hole Accretion Properties

The role that environment plays in determining observable properties of active galactic nuclei (AGN) is widely studied but, often times, confounding or contradictory. We seek to contribute to a sharper understanding of this relation using data in the radio, mid and near-IR, and optical regimes by investigating how strongly close environments of AGN affect luminosity, gas excitation levels, stellar mass, and redshift. The sample data set, sourced from VLA, WISE, 2MASS and SDSS surveys, comprises radio-selected galaxies matched to counterparts in the SDSS Stripe82 field where neighbouring galaxies are identified, optically. We use the surface density parameter i.e. ∑n, constrained in redshift and Ks magnitude for n=2 and n=5 separately to quantify the environments of our AGN and control samples thereby obtaining number-density measure for our sample. This measurement will occur in tandem with IR photometric analysis to ascertain the role of an AGN’s surroundings on its observed state.

Dharam Lal

The GMRT: Current Status and Ongoing Upgrade

The Giant Metrewave Radio Telescope (GMRT) is located near Pune, India. Today it is a major international facility for research in radio astronomy and astrophysics in the 150-1500 MHz frequency range and is a SKA pathfinder. It consists of 30 fully steerable antennas of 45 metre diameter each, spread over a 30 km region. It can be used both as an aperture synthesis array for continuum and spectral line imaging, as well as a phased array with a highly directive beam to study compact radio sources. We present the current status, highlight some of the recent achievements, and discuss the major upgrade presently underway. This talk consists of two parts: The first part is a short one comprising a few science highlights from the GMRT. The second part of the talk attempts to bring out a few details of the status and future plans of this upgrade.

Dharam Lal

FR I and FR II galaxies: New insights from radio and the X-ray data

Role of radio galaxies in the universe has been on upswing in recent years. Their colossal energy output over huge volumes is now widely believed to play a key role not only in the formation of galaxies and their super-massive blackholes, but also in the evolution of clusters of galaxies and, possibly, the cosmic web itself. Groups and clusters commonly contain radio galaxies, which eject large amounts of energy into their external environments. Its influence is to regulate gas cooling and galaxy evolution by an amount, which depends on energy ejected, mixing, and entrainment. Multi-frequency radio observations offer a method ("spectral-ageing") to constrain the formation model for X-shaped radio sources. In addition, X-ray observations (using unprecedented sensitivity of Chandra/XMM-Newton) provide constraints on the external (hot-gas) environments. We will present some recent insights from radio and X-ray studies and We will present the latest results from our ongoing effort to understand the nature of these sources.

Josh Marvil

ASKAP Commissioning and Early Science

I will present an overview and status update of the Australian Square Kilometer Array Pathfinder (ASKAP), and highlight recent and ongoing commissioning and scientific efforts with the Boolardy Engineering Test Array (BETA). BETA consists of six ASKAP antennas equipped with prototype phased array feeds, operates between 700-1800 MHz with a 300 MHz correlator, and electronically forms up to nine simultaneous beams. I will also discuss aspects of ASKAP early science and how these projects relate to large surveys such as EMU. The early science program will commence with a 12 antenna array equipped with second generation feeds and the capability to form up to 36 simultaneous beams.

Kim McAlpine

Where are the radio counterparts to the low- redshift far-infrared-luminous sources?

Mapping the star-formation history of the universe is one of the key science goals of future radio continuum surveys with SKA pathfinders telescopes and the SKA. Faint radio surveys are sensitive to synchrotron emission from star-forming galaxies (see e.g. Condon,1992) and offer the advantage over optical and near infrared surveys of being unaffected by dust extinction. The strongest evidence supporting the viability of radio surveys as tracers of star-formation in galaxies is the Far-Infrared Radio Correlation (FIRC), which indicates that radio emission is sensitive to the amount of star-formation taking place within its host galaxy and can be used to estimate a dust unbiased star-formation rate. The success of this technique thus relies heavily on a clear understanding of the FIRC and how it changes as a function of redshift, environment and star-formation rate. While current evidence suggests that the FIRC holds over a wide range of luminosities (Jarvis et al., 2010; Ivison et al., 2010), further work is needed to investigate this more thoroughly. Theoretical models of the FIRC suggest that galaxies may become radio dim, compared to the standard FIRC, at low star formation rates (e.g. Lacki et al. 2010). Such a departure would have important implications for the derivation of the star formation history of the universe from radio surveys. I will present results from a recent JVLA and KAT7 survey of a sample of 26 Herschel sources without radio counterparts in the NRAO VLA Northern Sky Survey (NVSS; Condon et al., 1998) in order to investigate the Far-Infrared Radio Correlation (FIRC) at low radio luminosities. The far-infrared (FIR) luminosity of these candidates is sufficiently bright that their non-detection in NVSS implies a departure from the standard FIRC. The availability of excellent multi-wavelenth data and accurate spectroscopic redshifts makes these ideal candidates to investigate the relationship between radio emission and star-formation rates at low radio luminosities.

Zolile Mguda

Ram pressure statistics for bent tail radio galaxies.

In this work we have used the MareNostrum Universe Simulation, a large scale, hydro- dynamic, non-radiative simulation in combination with a simple abundance matching approach to determine the ram pressure statistics for bent tail radio sources (BRTSs). The abundance matching approach allows us to determine the locations of all galaxies with stellar masses > 10^(11) h^(−1) solar masses in the simulation volume. Assuming ram pressure exceeding a critical value causes bent tail morphology, we compute the ratio of all galaxies exceeding the ram pressure limit (RPEX galaxies) relative to all galaxies in our sample. According to our model 50% of the RPEX galaxies at z = 0 are found in clusters with masses larger than 10^(14.5) h^(−1) solar masses the other half resides in lower mass clusters. Therefore, the appearance of bent tail morphology alone does not put tight constraints on the host cluster mass. In low mass clusters, with masses less than 10^14 h^(−1) solar masses, RPEX galaxies are confined to the central 500 kpc whereas in clusters of mass greater than 10^(15) h(−1) solar masses, they can be found at distances up to 1.5 Mpc. Only clusters with masses greater than 10^(15) h(−1) solar masses are likely to host more than one BTRS. Both criteria may prove useful in the search for distant, high mass clusters. We discuss how this work could be extended to incorporate mock catalogues and applied to constrain some of the current questions about bent-tail radio source environments.

Modhurita Mitra

Incorporation of antenna primary beam effects in calibration of wide-field, wide-band radio-interferometric data

The direction- and frequency-dependence of the gain pattern of the primary beam of an antenna pose one of the most challenging problems in wide-field, wide-band radio-interferometric calibration. I will present a new method of incorporating the primary beam during the calibration process, using a simulated beam model and the Multi-Term Multi-Frequency Synthesis algorithm. I will show an image obtained by applying this method to JVLA L-band data of the field around the radio source 3C147. This image has a dynamic range of 5,000,000:1, and the field has been successfully imaged out to the second sidelobe of the primary beam.

Tom Muxlow

The High Angular Resolution e-MERGE Galaxy Evolution Survey

The e-MERLIN Galaxy Evolution Survey (e-MERGE) is an ambitious multi-tiered legacy survey to exploit the unique combination of very high sensitivity and spatial resolution to study the formation and evolution of star-forming galaxies and AGN out to redshifts of z~5. These observations will provide a powerful, obscuration-independent tool for measuring the massive star formation and AGN activity in high-redshift galaxies, hence tracing the development of the stellar populations and the black hole growth in the first massive galaxies. With a resolution of 50-200 mas in C- and L-Bands, corresponding to ~ 0.5-1.5kpc at z ~ 1, e-MERLIN gives us our first truly reliable view of the distribution of star-formation within typical galaxies at the epoch where the bulk of the stars in the present-day Universe were being formed. In a previous study (Muxlow et al, 2005) it was shown that high angular resolution imaging of the distant radio source population with MERLIN is able to separate radio emission from AGN and star-forming regions. Thus in the deep e-MERGE Tier 1 observations of a 30 arcminute field centred on GOODS-N, combination EVN+e- MERLIN+JVLA imaging will disentangle the relative contributions of AGN and starformation - an essential step given the apparently simultaneous growth of the black holes and stellar populations in galaxies. With the central region of the Tier 1 field ultimately reaching sub-μJy noise levels, e-MERGE will image several thousand star-forming galaxies, and statistically characterize the nature of the sub-μJy radio population - which are the target population for the SKA. Initial results from e-MERLIN, and the JVLA on the e-MERGE Tier 1 region are presented here.

Iniyan Natarajan

Bayesian Inference for Radio Observations (BIRO)

We present a Bayesian formalism for analysing interferometric data in the visibility plane and its uses in inferring sub-resolution source structure and estimation of sky and instrumental parameters simultaneously. We also present the recently published results of applying this technique to WSRT simulations and the latest results obtained with SKA-VLBI simulations and real VLBI observations.

Emmanuel Ocran

The Nature of the MicroJy Source Population

We present a multiwavelength approach to studying faint radio sources drawn from the GMRT and JVLA surveys. Our radio sources are deep polarisation sensitive surveys of the extragalactic radio sky carried out to date, covering 0.1 deg$^{2}$ and 1 deg$^{2}$ at 5 GHz and 0.61 GHz for the JVLA and GMRT respectively. We combine radio data with multi-wavelength ancillary data to derive the distances and physical properties of the radio source population. In particular, we want to determine whether the emission at radio is dominated by an active nucleus at the centre of galaxies, powered by a massive black hole, or by radio emission from the disk of the galaxy powered by energy injection from stars.

Isabella Prandoni

Characterizing the faint AGN (RQ) component in deep radio fields: ongoing activity in eCDFS and GOODS-N

Radio-quiet (RQ) AGN show the presence of AGN activity in one or more bands of the electromagnetic spectrum (e.g., optical, mid-infrared, X-ray), but are characterized by relatively low radio-to-optical/IR flux density ratios and radio powers. For this reason they are typically found in optically (or IR/X-ray) selected samples. Recent results, however, show that the RQ AGN population starts to emerge in the deepest radio fields, at flux levels where star-forming galaxies (SFG) become dominant over radio-loud AGNs (<100 uJy). The origin of the radio emission in RQ AGN is still matter of debate. It has been proposed that RQ AGNs may be scaled down versions of RL AGNs, or alternatively, that their radio emission comes from ongoing star formation (SF) in the host galaxy. Another intriguing possibility is that AGN and SF processes both contribute to the total radio emission, in some relative proportion. The most direct way to probe the presence of AGN-driven radio emission in RQ AGN is the detection of embedded radio cores in the host galaxies, through very high resolution observations. In order to reliably separate radio structures on several scales, from AGN core/inner jets (<<1 kpc) to nuclear/disk starbursts (>1 kpc) in high redshift (z>1) galaxies, uJy imaging sensitivity together with mas resolution is clearly crucial. In my talk I will report about ongoing projects - undertaken in the framework of different collaborations - finalized at characterizing the faint AGN population (including the RQ AGN component) in radio deep fields and the role played by AGN feedback in the evolution of galaxies and star formation. Here I will focus on follow-up observations of two well-known radio fields: eCDFS and GOODS-N. An observing campaign is in progress with the LBA (Long Baseline Array) to search for possible radio cores in RQ-AGNs in the eCDFS field. I will report about the first of such detections. This is a tentative and preliminary result, but potentially very important, as it could challenge the scenario of purely SF-driven radio emission in RQ AGN. At lower resolution, but on a much larger statistical base, we can use eMERLIN and JVLA to provide 50-500 mas resolution images. In the framework of the eMERGE legacy programme (PI T. Muxlow), we are targeting the GOODS-N field at both 1.4 and 5 GHz. Here I will report on the ongoing analysis of an ultra-deep (1.5 uJy rms) JVLA mosaic observations at 5 GHz obtained with 0.5 arcsec resolution. Using existing 1.4 GHz and multi-band data, we are exploring the potential role of spectral index analysis at sub-arcsec resolution, to constrain the presence of AGN cores in moderate-to-high redshift (1

Isabella Prandoni

Characterizing the faint AGN (RQ) component in deep radio fields: ongoing activity and EMU perspectives

Radio-quiet (RQ) AGN show the presence of AGN activity in one or more bands of the electromagnetic spectrum (e.g., optical, mid-infrared, X-ray), but are characterized by relatively low radio-to-optical/IR flux density ratios and radio powers. For this reason they are typically found in optically (or IR/X-ray) selected samples. Recent results, however, show that the RQ AGN population starts to emerge in the deepest radio fields, at flux levels where star-forming galaxies (SFG) become dominant over radio-loud AGNs (<100 uJy). The origin of the radio emission in RQ AGN is still matter of debate. It has been proposed that RQ AGNs may be scaled down versions of RL AGNs, possibly displaying mini (or frustrated) radio jets, either associated to systems with very low accretion rates (like as FRI galaxies) or to efficiently accreting QSO-like systems. Alternatively, it has also been proposed that their radio emission comes from ongoing star formation (SF) in the host galaxy. Another intriguing possibility is that AGN and SF processes both contribute to the total radio emission, in some relative proportion. Radio observations alone cannot usually be used to distinguish between AGN and star formation activity in RQ AGNs, due to the lack of spatial resolution. As a consequence, current evidence in favor of one or the other type of activity come from indirect information, mostly based on multi-wavelength studies. On the other hand, the most direct way to probe the presence of AGN activity is the detection of embedded radio cores in the host galaxies through very high resolution observations. In order to reliably separate radio structures on several scales, from AGN core/inner jets (<<1 kpc) to nuclear/disk starbursts (>1 kpc) in high redshift (z>1) galaxies, uJy imaging sensitivity together with mas resolution is clearly crucial. In my talk I will report about ongoing projects - undertaken in the framework of different collaborations - finalized at characterizing the faint AGN population (including the RQ AGN component) in radio deep fields and the role played by AGN feedback in the evolution of galaxies and star formation. Here I will focus on follow-up observations of two well-known radio fields: eCDFS and GOODS-N. An observing campaign is in progress with the LBA (Long Baseline Array) to search for possible radio cores in RQ-AGNs in the eCDFS field. Even one single positive detection of a RQ AGN would represent a strong challenge to the scenario of purely SF-driven radio emission in RQ AGN. I will report about the first of such detections. This is a tentative and preliminary result, but potentially very important. At lower resolution, but on a much larger statistical base, we can use eMERLIN and JVLA to provide 50-500 mas resolution images. In the framework of the eMERGE legacy programme (PI T. Muxlow), we are targeting the GOODS-N field at both 1.4 and 5 GHz. Here I will report on the ongoing analysis of an ultra-deep (1.5 uJy rms) JVLA mosaic observations at 5 GHz obtained with 0.5 arcsec resolution. Using existing 1.4 GHz and multi-band data, we are exploring the potential role of spectral index analysis at sub-arcsec resolution, to constrain the presence of AGN cores in moderate-to-high redshift (1

Matt Prescott

325-MHz Luminosity Functions of Star Forming Galaxies and AGN

I will present radio luminosity functions (RLF) at 325-MHz for a sample of AGN and star forming galaxies by matching a 138 deg sq. radio survey conducted with the Giant Metrewave Radio Telescope (GMRT), with optical imaging from the Galaxy And Mass Assembly (GAMA) project. The RLF for star forming galaxies at 325-MHz, closely follows the local RLF found at 1.4-GHz. We find there is little evolution in low-luminosity AGN out to z =0.5.

Riona Ramraj

A Polarization Study of AGN in the Local Universe

Recent polarization studies have found an anticorrelation between the percentage polarization and flux density of radio sources. Since the flux density is related either to luminosity or redshift, this trend suggests either a change in magnetic properties with factors that correlate with luminosity or an evolutionary effect that changes with cosmic time, or both. We examine the 1.4 GHz polarization properties of a large well-defined sample of AGN in the Local Universe with known distances in an attempt to explore the apparent anticorrelation. Our study was conducted using a joint analysis of optical (6dFGRS and SDSS) and radio survey (NVSS) data. In addition to having a large sample size compared to previous studies, we go down to fainter radio luminosities (~10^{23} WHz^{-1}) than done before. In this talk, I will present the results obtained showing whether this trend does exists and if so, does it continue to fainter luminosities.

Solohery Randriamampandry

Far-Infrared-Radio Relations in Clusters and Groups at Intermediate Redshift

We present a multi-wavelength analysis of star-forming galaxies to shed new light on the evolution of the far-infrared-radio relations in intermediate redshift (0.3 < z < 0.6) galaxy clusters and galaxy groups. We have derived total infrared luminosities for a sample of cluster, group, and field galaxies through an empirical relation based on Spitzer MIPS 24 μm photometry. The radio flux densities were measured from deep Very Large Array 1.4 GHz radio continuum observations. We find that the ratio of far-infrared to radio luminosity for galaxies in an intermediate redshift clusters to be qFIR = 1.75±15 with a dispersion of 0.60. This value is comparable to that measured in low redshift clusters. A higher fraction of galaxies in clusters show an excess in their radio fluxes when compared to low redshift clusters, and corroborates previous evidence of a cluster enhancement of radio excess sources at this earlier epoch. Furthermore, we have investigated the properties of the far-infrared-radio correlation for a sample of galaxy groups in the COSMOS field. We find a lower percentage of radio-excess sources in groups as compared to clusters. This provides preliminary evidence that the number of radio-excess sources may depend on galaxy environment. We also find that a larger fraction of radio-excess sources in clusters are red sequence galaxies.

Glen Rees

Continuum Cosmology with ASKAP

In the last few years it has become readily apparent that the next generation of radio continuum surveys, are capable of placing significant constraints on the parameters of dark energy and modified gravity. Current plans to achieve these results make use of subtle cosmological effects such as the Integrated Sachs-Wolfe Effect, Cosmic Magnification and the spatial power spectrum to constrain a variety of cosmological models. We present recent work on a new cosmology pipeline that is being developed to measure these effects with the next generation of large area radio observations, as well as results from smaller, current surveys used during development (ATLAS, SPT, ASKAP-BETA). Finally, by comparing the actual cosmological sensitivity of recent surveys to their theoretical and simulated predictions, we investigate the impact that observational artefacts and imaging processes have on the cosmological sensitivity of next generation radio telescopes.

Wiphu Rujopakarn

Resolving the Obscured Cosmic Accretion History and Modes of Galaxy Assembly

Dust obscuration has hidden at least half of the cosmic accretion activity and concealed the most intense sites of star formation during the peak epoch for both processes at 1 < z < 3. Centimetric radio interferometry is the only means of identifying the AGNs and tracing star-forming activities at sub-arcsecond resolution, in an extinction-independent manner. I will discuss the use of radio survey to study star formation and AGN at 1 < z < 3, focusing on the early results from our ultra-deep 4-8 GHz Jansky VLA (JVLA) radio observations at 0.3" resolution in the UDS and HUDF fields. The goals of these surveys are to spatially resolve the structure of star-forming galaxies, and to combine the radio data with panchromatic observations to produce a complete census of AGN out to z = 3. The ongoing survey in the HUDF, in particular, will reach 0.3 microJy/beam RMS and will provide a definitive radio dataset for spatially-resolved, ultra-deep, broadband extragalactic studies, providing a first glimpse of what SKA will bring.

Mario Santos

Cosmology with large radio continuum surveys

A new generation of radio telescopes is being developed with high sensitivity and large fields of view, making them exquisite "machines" for cosmology. All sky continuum surveys with huge numbers of radio galaxies should be one of the most easily accessible data products for Cosmology. This in turn will allow powerful constraints not only on "standard" cosmological parameters, such as dark energy, but also beyond that, such as primordial non-Gaussianity, modified gravity or other effects on ultra-large scales. I will review the main constraints we can expect from these telescopes, such as MeerKAT, ASKAP, APERTIF and SKA1-MID, and describe the approaches we will need to take in order to extract this information.

Nick Seymour

ASKAP and MWA Synergy: A New Era of Broadband Radio Astronomy

ASKAP and MWA are both conducting unprecedented all southern sky surveys at mid (1.1-1.4GHz) and low (80-230MHz) radio frequencies which when combined with each other will provide a unique data set of broadband radio SEDs. I will summarise the continuum surveys being conducted by ASKAP and MWA and I will present unique science to be obtained from such a combined radio data set. I will demonstrate that only ~1/3 of all radio sources are power-laws over many orders of magnitude. Most broadband radio SEDs show at least one degree of curvature (i.e. can be well fit by a quadratic in log-log space) and some even show more complex SEDs. I will present novel diagnostic techniques of these radio SEDs and how this can be used to select distinct populations. I will also show specific examples for a subset of radio sources.

Veeresh Singh

Unveiling the population of high-redshift radio galaxies using deep radio continuum surveys

Ultra Steep Spectrum (USS) radio sources are one of the efficient tracers of powerful High-z Radio Galaxies (HzRGs). We characterize multi-band optical, near-IR and mid-IR properties of a USS sample derived from deep 325 MHz GMRT and 1.4 GHz VLA surveys. Our study shows that the criterion of ultra steep spectral index remains a reasonably efficient method to select high-z sources even at sub-mJy flux densities. In addition to powerful HzRG candidates, our faint USS sample also contains populations of weaker radio-loud AGNs potentially hosted in dusty galaxies. Results of our study will be presented in the context of upcoming deeper radio continuum surveys from SKA and its pathfinders.

Jeroen Stil

The power of N

Stacking is a potentially powerful tool to investigate classes of objects whose inpidual flux densities may fall below the formal detection limit of a survey.For large samples of size N = 10^4 to 10^5, the noise has been shown to decrease as the square root of N. Whether the apparent noise in the stacked image is a good indication of the accuracy of the flux density derived from stacking, depends on one's ability to limit the effect of systematic errors. These may arise for example from position errors, coarse gridding of the survey images, finite source dimensions, signal-to-noise-ratio dependent bias, and selection bias in the input catalog. With a complete assessment of these challenges, stacking not only allows us to derive the median flux density of samples of faint sources, but also exploit wide-band capability of radio surveys to extract spectral information that is otherwise not accessible. Key to this argument is that sample sizes easily exceed the number of frequency channels by orders of magnitude. The theoretical sensitivity of stacking a sample of sources in a single frequency channel is therefore much larger than the band-averaged Stokes I sensitivity. This opens the possibility to investigate the in-band spectral index from median stacking, and polarization properties as a function of frequency, down to the Stokes I detection limit of the survey itself.

C. Tasse & O.Smirnov (presenting author)

Kalman Filters, Wirtinger Calculus, Faceting and Baseline-dependent Averaging for WFWB Calibration and Imaging

We'll present some new algorithmic developments for dealing with wide-field, wide-band interferometric data. The use of Wirtinger calculus allows for a compact reformulation of the complex gain calibration problem and leads to a new family of direction-dependent calibration algorithms. One of these is KAFCA, a Kalman filter-inspired approach for very rapid DD solutions, suitable for anj "online calibration" regime. These solutions can then applied via a new facet-based imager called DDFacet, which uses baseline-dependent averaging to substantially reduce gridding time per facet. We show an application of this to deep LOFAR observations of the Bootes field.

Mattia Vaccari

HELP-ing Radio Continuum Surveys : The Herschel Extragalactic Legacy Project

HELP-ing Radio Continuum Surveys : The Herschel Extragalactic Legacy Project The Herschel Extragalactic Legacy Project (HELP, http://herschel.sussex.ac.uk/) is a 4-year (2014-2017) 2.5 MEuro project funded by the EC FP7-SPACE programme whose aim is to produce homogeneous multi-wavelength value-added source catalogs spanning Herschel's wide-area extragalactic surveys for a total ~1000 deg$^2$. Building upon existing data reduction best practices at different wavelengths and developing new tools to identify the most likely sources of far-infrared emission in Herschel confused maps, HELP will bridge the gap betwwen COSMOS and SDSS and produce a multi-wavelength database enabling galaxy evolution studies of the distant Universe over the largest scales. This will provide an accessible resource for the astronomical community to mine for decades to come, a lasting legacy of many thousands of hours on space telescopes as well as thousands of nights on ground based telescopes, building a solid foundation for future space missions and ground-based observatory projects. In my talk I will introduce HELP, its main objectives and hardest challenges, report on its status and outline how it will benefit radio continuum surveys.

Tessa Vernstrom

MircoJansky Radio Sources: Counts, Confusion, and Catalogues

Understanding the faint extragalactic radio sky, from both discrete and diffuse emission, has important implications for studying galaxy evolution, galaxy populations, the star formation history, and cluster emission, in addition to being important for designing future deep radio surveys. Statistical techniques such as confusion P(D) analysis and stacking are key for pushing measurements and constraints past current survey detection limits. Using deep 3 GHz data from the Karl G. Jansky Very Large Array (VLA) we have used confusion and P(D) to obtain source count estimates into the sub-microJy regime, as well as the extragalactic contribution to the cosmic radio background temperature from these sources. Using additional VLA time at a higher resolution, we have constructed a catalogue of sources in the Lockman Hole using comparably deep 8 arcsecond and 2.75 arcsecond resolution images. Combined with simulations, we examine the effect of resolution on source fitting uncertainties and corrections, source blending, completeness, and false detections. The catalogues show the power of P(D) to match traditional counting methods. With the use of the VLA 2 GHz bandwidth, and cross-matching catalogues with other wavelengths, we investigate the spectral indices, redshifts, and optical colours of microJy sources. This work, in addition to complementary work with diffuse emission, demonstrate techniques, and possible challenges, as well as new deep measurements that will be important for the future SKA and upcoming SKA pathfinder (and possible new VLA) surveys.

Yogesh Wadadekar

Deep continuum surveys with the GMRT at 325 MHz

We have carried out a deep (150 micro Jy rms) P-band, continuum imaging survey of about 40 square degrees of sky in the XMM-LSS, Lockman Hole and ELAIS-N1 fields with the GMRT. Our deep radio data, combined with deep archival observations in the X-ray (XMM/Chandra), optical (SDSS, CFHTLS, VIPERS, PRIMUS), near-infrared (UKIDSS, VISTA/VIDEO), mid-infrared (Spitzer/SWIRE, Spitzer/SERVS) and far-infrared (Spitzer/SWIRE, Herschel/HerMES) enable us to obtain an accurate census of star-forming and active galaxies out to z~2. This panchromatic coverage enables accurate determination of photometric redshifts and accurate modeling of the spectral energy distribution. We have used our new GMRT data to pursue a number of scientific investigations. In the XMM-LSS field, we have studied the radio-FIR correlation in blue-cloud galaxies out to z ~ 1 using image stacking (Basu et al. 2015), identified and studied a sample of high redshift radio galaxies (Singh et al. 2014) and investigated in detail an extremely rare relic giant radio galaxy caught in its dying phase at z ~ 1.3 (Tamhane et al. 2015). All these studies exploit the full potential of the GMRT data by leveraging the availability of panchromatic archival observations in all bands from X-ray to the radio. We are shortly releasing the GMRT catalog of the XMM-LSS field to the community (Wadadekar et al. 2015) to maximise the legacy value of our data.

Imogen Whittam

Exploring the faint source population at 15.7 GHz

I will present results from a multi-wavelength study of the faint source population at 15.7 GHz, a previously unexplored parameter space. A complete sample of sources with flux densities > 0.5 mJy is selected from the Tenth Cambridge (10C) survey and matched to several lower frequency radio catalogues. We find a significant change in spectral index with flux density; the proportion of flat spectrum sources increases dramatically below 1 mJy. This change is not predicted by the SKADS Simulated Skies, highlighting the need to study this population of faint, high-frequency sources. The radio catalogue is matched to a range of multi-wavelength data, and we find that the majority of the 10C sources are radio-loud galaxies. These sources are split into high-excitation and low-excitation radio galaxies (HERGs and LERGs), and we find that the HERGs tend to have flatter spectra, higher flux densities and be at higher redshifts than the LERGs. We have used new observations to extend this study to fainter flux densities, calculating the 15.7-GHz radio source count down to 0.1 mJy, a factor of five deeper than previous studies.

Jonathan Zwart

Astronomy below the Survey Threshold

Astronomy at or below the survey threshold has expanded significantly since the publication of the original SKA science case in 1999 and its update in 2004. The techniques in this regime may be broadly (but far from exclusively) defined as confusion or P(D) analyses (analyses of one-point statistics), and stacking, accounting for the flux-density distribution of noise-limited images co-added at the positions of objects detected/isolated in a different waveband. I will discuss the relevant issues, present some examples of recent analyses, and consider some of the consequences for the design and use of surveys with the SKA and its pathfinders.