A new era in radio astronomy will begin with the upcoming large-scale surveys planned at the Australian Square Kilometre Array Pathfinder (ASKAP). ASKAP started its Early Science programme in October 2017 and several target fields were observed during the array commissioning phase. The Scorpio field was the first observed in the Galactic Plane in Band 1 (792–1 032 MHz) using 15 commissioned antennas. The achieved sensitivity and large field of view already allow to discover new sources and survey thousands of existing ones with improved precision with respect to previous surveys. Data analysis is currently ongoing to deliver the first source catalogue. Given the increased scale of the data, source extraction and characterisation, even in this Early Science phase, have to be carried out in a mostly automated way. This process presents significant challenges due to the presence of extended objects and diffuse emission close to the Galactic Plane.

In this context, we have extended and optimised a novel source finding tool, named Caesar, to allow extraction of both compact and extended sources from radio maps. A number of developments have been done driven by the analysis of the Scorpio map and in view of the future ASKAP Galactic Plane survey. The main goals are the improvement of algorithm performances and scalability as well as of software maintainability and usability within the radio community. In this paper, we present the current status of Caesar and report a first systematic characterisation of its performance for both compact and extended sources using simulated maps. Future prospects are discussed in the light of the obtained results.

For decades, the deceptive simplicity of the radius $R_{\rm e}$, enclosing an arbitrary 50% of a galaxy’s light, has hamstrung the understanding of early-type galaxies (ETGs). Half a century ago, using these ‘effective half-light’ radii from de Vaucouleurs’ $R^{1/4}$ model, Sérsic reported that bright ETGs follow the relation $\mathfrak{M}_B\propto2.5\log R_{\rm e}$; and consequently, one has that $\langle\mu\rangle_{\rm e}\propto2.5\log R_{\rm e}$ and $\mu_{\rm e}\propto2.5\log R_{\rm e}$, where $\mu_{\rm e}$ and $\langle\mu\rangle_{\rm e}$ are the effective surface brightness at $R_{\rm e}$ and the mean effective surface brightness within $R_{\rm e}$, respectively. Sérsic additionally observed an apparent transition which led him to advocate for a division between what he called dwarf and giant ETGs; a belief frequently restated to occur at $\mathfrak{M}_B \approx -18$ mag or $n\approx 2.5$. Here, the location of this false dichotomy in diagrams using ‘effective’ parameters is shown to change by more than 3 mag simply depending on the arbitrary percentage of light used to quantify a galaxy’s size. A range of alternative radii are explored, including where the projected intensity has dropped by a fixed percentage plus a battery of internal radii, further revealing that the transition at $\mathfrak{M}_B\approx -18$ mag is artificial and does not demark a boundary between different physical processes operating on the ETG population.

The above understanding surrounding the effective radius $R_{\rm e}$ is of further importance because quantities such as dynamical mass $\sigma^2R/G$, gravitational-binding energy $GM^2/R$, acceleration $GM/R^2$, and the ‘Fundamental Plane’ also depend on the arbitrary percentage of light used to define R, with implications for dark matter estimates, galaxy formation theories, compact massive galaxies, studies of peculiar velocity flows, and more. Finally, some of the vast literature which has advocated for segregating the ETG population at $\mathfrak{M}_B \approx -18$ mag ($M\approx1$–$2\times10^{10}\,{\rm M}_{\odot}$) is addressed, and it is revealed how this pervasive mindset has spilled over to influence both the classical bulge versus pseudobulge debate and recently also correlations involving supermassive black hole masses.

We study a class of Newtonian models for the deformations of non-magnetised neutron stars during their spin-down. All the models have an analytical solution which allows to easily grasp the dependence of the strain on the star’s main physical quantities, such as radius, mass, and crust thickness.

We first use the model proposed by Franco, Link, and Epstein that depicts the star as made of a fluid core and an elastic crust with the same density, to compare the response to a decreasing centrifugal force on stars having different masses and equations of state. We find that the strain angle is peaked at the equator and its maximum value decreases as a function of the mass.

Afterwards, we introduce a second, more refined, model in which the core and the crust have different densities, and the gravitational potential of the deformed body is self-consistently accounted for. The strain angle is still a decreasing function of the stellar mass, but now its maximum value is typically peaked at the poles and is larger (by a factor of four) than the corresponding value in the one-density model.

Finally, within the present analytic approach, we evaluate the impact of the Cowling approximation: when the perturbations of the gravitational potential are neglected, we find an underestimation of the centrifugal effect on the star, since the strain angle is about 40% of the one obtained with the complete model.

Rotating Radio Transients (RRATs) represent a relatively new class of pulsar, primarily characterised by their sporadic bursting emission of single pulses on time scales of minutes to hours. In addition to the difficulty involved in detecting these objects, low-frequency ($ \lt 300\,\text{MHz}$) observations of RRATs are sparse, which makes understanding their broadband emission properties in the context of the normal pulsar population problematic. Here, we present the simultaneous detection of RRAT J2325−0530 using the Murchison Widefield Array (154 MHz) and Parkes radio telescope ($1.4\,\text{GHz}$). On a single-pulse basis, we produce the first polarimetric profile of this pulsar, measure the spectral index ($\alpha={-2.2\pm 0.1}$), pulse energy distributions, and present the pulse rates in the context of detections in previous epochs. We find that the distribution of time between subsequent pulses is consistent with a Poisson process and find no evidence of clustering over the $\sim\!1.5\,\text{h}$ observations. Finally, we are able to quantify the scintillation properties of RRAT J2325−0530 at 1.4 GHz, where the single pulses are modulated substantially across the observing bandwidth, and show that this characterisation is feasible even with irregular time sampling as a consequence of the sporadic emission behaviour.

We present the second data release (DR2) of the SkyMapper Southern Survey, a hemispheric survey carried out with the SkyMapper Telescope at Siding Spring Observatory in Australia, using six optical filters: u, v, g, r, i, z. DR2 is the first release to go beyond the $\sim\!18$ mag (10$\sigma$) limit of the Shallow Survey released in the first data release (DR1), and includes portions of the sky at full survey depth that reach $>\!21$ mag in g and r filters. The DR2 photometry has a precision as measured by internal reproducibility of 1% in u and v, and 0.7% in griz. More than 21 000 $\deg^2$ have data in some filters (at either Shallow or Main Survey depth) and over 7 000 $\deg^2$ have deep Main Survey coverage in all six filters. Finally, about 18 000 $\deg^2$ have Main Survey data in i and z filters, albeit not yet at full depth. The release contains over 120 000 images, as well as catalogues with over 500 million unique astrophysical objects and nearly 5 billion individual detections. It also contains cross-matches with a range of external catalogues such as Gaia DR2, Pan-STARRS1 DR1, GALEX GUVcat, 2MASS, and AllWISE, as well as spectroscopic surveys such as 2MRS, GALAH, 6dFGS, and 2dFLenS.

We describe the design and deployment of GREENBURST, a commensal Fast Radio Burst (FRB) search system at the Green Bank Telescope. GREENBURST uses the dedicated L-band receiver tap to search over the 960–1 920 MHz frequency range for pulses with dispersion measures out to $10^4\ \rm{pc\,cm}^{-3}$. Due to its unique design, GREENBURST is capable of conducting searches for FRBs when the L-band receiver is not being used for scheduled observing. This makes it a sensitive single pixel detector capable of reaching deeper in the radio sky. While single pulses from Galactic pulsars and rotating radio transients will be detectable in our observations, and will form part of the database we archive, the primary goal is to detect and study FRBs. Based on recent determinations of the all-sky rate, we predict that the system will detect approximately one FRB for every 2–3 months of continuous operation. The high sensitivity of GREENBURST means that it will also be able to probe the slope of the FRB fluence distribution, which is currently uncertain in this observing band.

SN1991bg-like supernovae are a distinct subclass of thermonuclear Type Ia supernovae (SNe Ia). Their spectral and photometric peculiarities indicate that their progenitors and explosion mechanisms differ from ‘normal’ SNe Ia. One method of determining information about supernova progenitors we cannot directly observe is to observe the stellar population adjacent to the apparent supernova explosion site to infer the distribution of stellar population ages and metallicities. We obtain integral field observations and analyse the spectra extracted from regions of projected radius $\sim\,\text{kpc}$ about the apparent SN explosion site for 11 91bg-like SNe in both early- and late-type galaxies. We utilise full-spectrum spectral fitting to determine the ages and metallicities of the stellar population within the aperture. We find that the majority of the stellar populations that hosted 91bg-like supernovae have little recent star formation. The ages of the stellar populations suggest that that 91bg-like SN progenitors explode after delay times of >6 Gyr, much longer than the typical delay time of normal SNe Ia, which peaks at $\sim$1 Gyr.

In recent years, the discovery of massive quasars at $z\sim7$ has provided a striking challenge to our understanding of the origin and growth of supermassive black holes in the early Universe. Mounting observational and theoretical evidence indicates the viability of massive seeds, formed by the collapse of supermassive stars, as a progenitor model for such early, massive accreting black holes. Although considerable progress has been made in our theoretical understanding, many questions remain regarding how (and how often) such objects may form, how they live and die, and how next generation observatories may yield new insight into the origin of these primordial titans. This review focusses on our present understanding of this remarkable formation scenario, based on the discussions held at the Monash Prato Centre from November 20 to 24, 2017, during the workshop ‘Titans of the Early Universe: The Origin of the First Supermassive Black Holes’.

We present TreeFrog, a massively parallel halo merger tree builder that is capable comparing different halo catalogues and producing halo merger trees. The code is written in c++11, use the MPI and OpenMP API’s for parallelisation, and includes python tools to read/manipulate the data products produced. The code correlates binding energy sorted particle ID lists between halo catalogues, determining optimal descendant/progenitor matches using multiple snapshots, a merit function that maximises the number of shared particles using pseudo-radial moments, and a scheme for correcting halo merger tree pathologies. Focusing on VELOCIraptor catalogues for this work, we demonstrate how searching multiple snapshots spanning a dynamical time significantly reduces the number of stranded halos, those lacking a descendant or a progenitor, critically correcting poorly resolved halos. We present a new merit function that improves the distinction between primary and secondary progenitors, reducing tree pathologies. We find FOF accretion rates and merger rates show similar mass ratio dependence. The model merger rates from Poole, et al. [2017, 472, 3659] agree with the measured net growth of halos through mergers.

The Murchison Widefield Array is a low-frequency Square Kilometre Array precursor located at the Murchison Radio-astronomy Observatory in Western Australia. Primarily designed as an imaging telescope, but with a flexible signal path, the capabilities of this telescope have recently been extended to include off-line incoherent and tied-array beam formation using recorded antenna voltages. This has provided the capability for high-time and frequency resolution observations, including a pulsar science program. This paper describes the algorithms and pipeline that we have developed to form the tied-array beam products from the summation of calibrated signals of the antenna elements, and presents example polarimetric profiles for PSRs J0437-4715 and J1900-2600 at 185 MHz.

Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a ‘Phase A’ concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100–350 $\mu$m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 $\mu$m images will also have a factor $\sim $30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.

Epoch of Reionisation (EoR) data analysis requires unprecedented levels of accuracy in radio interferometer pipelines. We have developed an imaging power spectrum analysis to meet these requirements and generate robust 21 cm EoR measurements. In this work, we build a signal path framework to mathematically describe each step in the analysis, from data reduction in the Fast Holographic Deconvolution (FHD) package to power spectrum generation in the εppsilon package. In particular, we focus on the distinguishing characteristics of FHD/εppsilon: highly accurate spectral calibration, extensive data verification products, and end-to-end error propagation. We present our key data analysis products in detail to facilitate understanding of the prominent systematics in image-based power spectrum analyses. As a verification to our analysis, we also highlight a full-pipeline analysis simulation to demonstrate signal preservation and lack of signal loss. This careful treatment ensures that the FHD/εppsilon power spectrum pipeline can reduce radio interferometric data to produce credible 21 cm EoR measurements.

Polarimetric studies of pulsars at low radio frequencies provide important observational insights into the pulsar emission mechanism and beam models, and probe the properties of the magneto-ionic interstellar medium (ISM). Aperture arrays are the main form of next-generation low-frequency telescopes, including the Murchison Widefield Array (MWA). These require a distinctly different approach to data processing (e.g. calibration and beamforming) compared to traditional dish antennas. As the second paper of this series, we present a verification of the MWA’s pulsar polarimetry capability, using two bright southern pulsars, PSRs J0742–2822 and J1752–2806. Our observations simultaneously cover multiple frequencies (76–313 MHz) and were taken at multiple zenith angles (ZA) during a single night for each pulsar. We show that the MWA can be reliably calibrated for ZA ≲45° and frequencies ≲270 MHz. We present the polarimetric profiles for PSRs J0742–2822 and J1752–2806 at frequencies lower than 300 MHz for the first time, along with an analysis of the linear polarisation degree and pulse profile evolution with frequency. For PSR J0742–2822, the measured degree of linear polarisation shows a rapid decrease at low frequencies, in contrast with the generally expected trend, which can be attributed to depolarisation effects from small-scale, turbulent, magneto-ionic ISM components. This effect has not been widely explored for pulsars in general and will be further investigated in future work.