Jasper V. Wall

EMU: Evolutionary Map of the Universe

EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ~10 μJy/beam) radio continuum survey of the entire Southern sky at 1.3 GHz, extending as far North as +30° declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z ~ 1, powerful starbursts to even greater redshifts, and active galactic nuclei to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.

Extragalactic radio source evolution under the dual-population unification scheme

We show that a dual-population unification scheme provides a successful paradigm with which to describe the evolution and beaming of all bright extragalactic radio sources. The paradigm consists of two intrinsic radio-source populations, based on the two distinct radio-galaxy morphologies of Fanaroff-Riley classes I and II. These represent the ‘unbeamed’ or ‘side-on’ parent populations of steep radio spectra; the ‘beamed’ source types including flat-spectrum quasars and BLLac objects, arise through the random alignment of their radio-axis to our line-of-sight where Dopplerbeaming of the relativistic radio jets produces highly anisotropic radio emission. We develop the model in two stages. In the first stage the source space density as a function of cosmic epoch is determined for the two parent populations, and for this we use low-frequency source-count and identification data to avoid biases due to Doppler-enhanced radio emission. The second stage defines the beaming models for each population, using high-frequency survey data and in particular the 5-GHz source count in which at high flux densities the flat- and steep-spectrum sources contribute in similar measure. We assume that the flat-spectrum objects, quasars and BLLac objects are ‘beamed’ versions of FRI and FRII objects in which the close alignment of radio-axis with line-of-sight has changed the radio appearance into a core-dominated (flat-spectrum) object. We adopt a simple parameterisation of the beaming, orient the parent populations at random with a Monte-Carlo process, and use a minimisaton process to determine beaming parameters which yield a best fit to the 5-GHz souce count. The best-fit parameters are found to be in good agreement with those measured observationally for individual radio sources. In this, the model accurately reproduces the change in source-count form with frequency. Indeed the unified-scheme paradigm has great predictive power, and we show how the model successfully describes several additional and independent data sets.

Science with the Australian Square Kilometre Array Pathfinder

The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline the ASKAP project and summarise its headline science goals as defined by the community at large.

The Parkes quarter-Jansky flat-spectrum sample: III. Space density and evolution of QSOs

We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the present day to epochs corresponding to redshifts ∼1. We draw attention to a selection effect due to spread in spectral shape that may have misled other investigators to consider the apparent similarities in shape of luminosity functions in different redshift shells as evidence for luminosity evolution. To examine the evolution at redshifts beyond 3, we develop a model-independent method based on the Vmax test using each object to predict expectation densities beyond z = 3. With this we show that a diminution in space density at z > 3 is present at a significance level >4σ. We identify a severe bias in such determinations from using flux-density measurements at epochs significantly later than that of the finding survey. The form of the diminution is estimated, and is shown to be very similar to that found for QSOs selected in X-ray and optical wavebands. The diminution is also compared with the current estimates of star-formation evolution, with less conclusive results. In summary we suggest that the reionization epoch is little influenced by powerful flat-spectrum QSOs, and that dust obscuration does not play a major role in our view of the QSO population selected at radio, optical or X-ray wavelengths.

Variance and Skewness in the FIRST Survey

We investigate the large-scale clustering of radio sources in the FIRST 1.4-GHz survey by analysing the distribution function (counts in cells). We select a reliable sample from the the FIRST catalogue, paying particular attention to the problem of how to define single radio sources from the multiple components listed. We also consider the incompleteness of the catalogue. We estimate the angular two-point correlation function

Measurement of the angular correlation function of radio galaxies from the NRAO VLA Sky Survey

w(\theta)

A velocity dipole in the distribution of radio galaxies

, the variance

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

\Psi_2

The Parkes quarter-Jansky flat-spectrum sample - I. Sample selection and source identifications

, and skewness

The CORALS survey - II. Clues to galaxy clustering around QSOs from

\Psi_3