Kilometre Array Radio Telescope Research Articles

First look at the topology of reionisation redshifts in models of the epoch of reionisation

Context. During the epoch of reionisation (EoR), the first stars and galaxies appeared while creating ionised bubbles that eventually percolated near z ∼ 6. These ionised bubbles and percolation process are closely scrutinised today because observations of neutral hydrogen will be carried on in the next decade with the Square Kilometre Array radio telescope, for instance. In the meantime, EoR studies are performed in semi-analytical and fully numerical cosmological simulations to investigate the topology of the process, for instance. Aims. We analyse the topology of EoR models by studying regions that are under the radiative influence of ionisation sources. These regions are associated with peak patches of the reionisation redshift field, for which we measure the general properties such as their number, size, shape, and orientation. We aim to gain insights into the geometry of the reionisation process and its relation to the matter distribution, for example. We also assess how these measurements can be used to quantify the effect of physical parameters on the EoR models or the differences between fully numerical simulations and semi-analytical models. Methods. We used the framework of Morse theory and persistent homology in the context of the EoR, which was investigated via the DisPerSE algorithm on gas density and redshift of reionisation maps. We analysed different EoR scenarios with semi-analytical 21cmFAST and fully numerical EMMA simulations. Results. We can distinguish between EoR models with different sources using simple analyses of the number, shape, and size distributions of the reionisation redshift patches. For every model (of the semi-analytical and fully numerical simulations), we statistically show that these bubbles are rather prolate and aligned with the underlying gas filaments. Moreover, we briefly highlight that the percolation process of HII bubbles during the EoR can be followed by studying the reionisation redshift fields with different persistence thresholds. Finally, we show that fully numerical EMMA simulations can be made consistent with 21cmFAST models in this topological framework as long as the source distribution is diffuse enough.

Indiscipline as Method: From Telescopes to Ventilators in Times of Covid

There is no unproblematic way to study things as “African”, yet an epistemologically situated approach based on concrete technological projects situated in Africa and their social and political implications offers an important account of the intersection of the Fourth Industrial Revolution and African Studies. We explore this perspective through the notion of “indiscipline” using the Square Kilometre Array radio telescope project (SKA) based in South Africa as a case study through which to observe “indiscipline” as a methodological approach to technoscience at work. Indiscipline helps frame the socio-technical (by)products of astrophysics and engineering, and we present the production of ventilators for COVID-19 patients as an example of how the design of mega-science projects can become entangled with the dynamic concerns of society. Our conclusion elaborates on the politics of large technological systems, opening up a conversation on the intersection of science and society in the context of the Fourth Industrial Revolution in African settings, using the template of experiences with the SKA and the National Ventilator Project in South Africa.

Cosmopolitan Karoo: Land, Space and Place in the Shadow of the Square Kilometre Array

Drawing on insights from critical cosmopolitanism and human geography, this article reflects on the tensions between the local and the global, and ‘space’ and ‘place’ within large areas of South Africa’s arid Karoo region designated as Astronomy Advantage Areas (AAAs), and considers their significance for contemporary identity claims and relationships to land. To date most of the Northern Cape, encompassing some 30 per cent of South Africa, has been declared an AAA in terms of the 2007 Astronomy Geographic Advantage Act. The proclamation of AAAs is intended to facilitate the development of astronomy in the region, centred on the optical South African Large Telescope (SALT) in the south and an internationally networked mega-radio-astronomy project, the Square Kilometre Array radio telescope (SKA), in the centre. The core site of the SKA project, the focus of this article, is being built on a large block of formerly white-owned farms that have been bought by the state. Radio astronomy’s specific requirements for minimising radio frequency interference around its operating sites make co-existence with other land uses (including but not only agriculture) more difficult than in the case of optical astronomy, and local townspeople feel aggrieved that their expectations of development have not been adequately met. In addressing these concerns the SKA has prioritised negotiations with national rather than local organisations, including the San Council, claiming to represent the descendants of the hunter-gatherers whose land this once was, and Agri-SA, representing commercial farmers nationally. To date the promotion of astronomy in the Karoo is premised on a metropolitan view of this region as politically and economically marginal: effectively empty space, to be put to good use in the service of global science and national development, rather than a deeply historical place, long embedded in trans-local dynamics and facing significant, largely unresolved social challenges today.

From the ‘Merino Revolution’ to the ‘Astronomy Revolution’: Land Alienation and Identity in Carnarvon, South Africa

The establishment of an astronomy reserve around the core site of the Square Kilometre Array radio telescope marks the beginning of an epochal shift away from commercial sheep farming in the upper Karoo. In this article, I reflect on the significance of this ‘astronomy revolution’ by exploring the ways in which land is central to dynamics of identification, shaping social hierarchies and development expectations. The article uses archival and ethnographic sources to explore the case of Carnarvon. It contextualises the current land-use change to astronomy in the social history of the town, addressing the set of events that marked an earlier epochal change: the transition from communal to commercial sheep farming, often called the ‘merino revolution’. The history of land alienation accompanying this earlier transition resurfaces in current claims lodged through the post-apartheid land restitution programme, which intersect in complex ways with the current land-use change to astronomy. The article identifies a central tension in the ‘astronomy revolution’, which undermines claims to redress local historical inequalities while promoting identification with a broader national and global development priority.

Optimal identification of H ii regions during reionization in 21-cm observations

The ability of the future low frequency component of the Square Kilometre Array radio telescope (SKA-Low) to produce tomographic images of the redshifted 21-cm signal will enable direct studies of the evolution of the sizes and shapes of ionized regions during the Epoch of Reionization. However, a reliable identification of ionized regions in noisy interferometric data is not trivial. Here, we introduce an image processing method known as superpixels for this purpose. We compare this method with two other previously proposed ones, one relying on a chosen threshold and the other employing automatic threshold determination using the K-Means algorithm. We use a correlation test and compare power spectra and bubble size distributions to show that the superpixels method provides a better identification of ionized regions, especially in the case of noisy data. We also describe some possible additional applications of the superpixel method, namely the derivation of the ionization history and constraints on the source properties in specific regions.

AN EVALUATION OF THE EFFECTIVENESS OF OBSERVATION CAMERA PLACEMENT WITHIN THE MEERKAT RADIO TELESCOPE PROJECT

A recent development within the MeerKAT sub-project of the Square Kilometre Array radio telescope network was the placement of a network of three observation cameras in pursuit of two specific visibility objectives. In this paper, we evaluate the effectiveness of the locations of the MeerKAT observation camera network according to a novel multi-objective geographic information systems-based facility location framework. We find that the configuration chosen and implemented by the MeerKAT decision-makers is of very high quality, although we are able to uncover slightly superior alternative placement configurations. A significant amount of time and effort could, however, have been saved in the process of choosing the appropriate camera sites, had our solutions been available to the decision-makers.

A broadband self-calibrated RMS power detector embedded in a square kilometre array receiver

In this work, the performance of a broadband self-calibrated root-mean-square (RMS) power detector (PD) embedded in a square kilometre array radio telescope receiver is reported. The power detection function was obtained using MOSFET square-law characteristics in saturation. The PD is automatically calibrated to compensate for circuit component mismatches and to improve its sensitivity. The calibration circuit adjusts input transistor threshold voltages by controlling bulk terminal voltages to reduce mismatches. Measurements demonstrate a power-detection range from −39.6 to −20 dBm while consuming 1.5 mW. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1426–1432, 2015

Small Science: View from Developing Nations

In the Editorial “The end of ‘small science’?” (28 September, p. [1583][1]), B. Alberts asks whether the era of “small-science” projects is coming to an end. He hopes not. I share this sentiment, from the perspective of developing countries where science budgets are small. It seems clear, however, that big, headline-grabbing projects will likely continue to increase. Thus, the leaders of these projects should seize the opportunity to enable and inspire the next generation of scientists in developing countries. Developing countries do not have the budgets to initiate such “big-science” projects, but they do have ample talent to contribute. Unfortunately, ENCODE—just like the Human Genome Project and others—included scientists from only one developing nation (China). An exceptional example of integrating developing countries into big-science projects is the decision to award the Square Kilometre Array radio telescope to Africa ([ 1 ][2]). The ripple effects in the media, government, and rest of society are noticeable in South Africa and promising for public support for science. Such support is critical if we are to bridge the gap between science in developed and developing countries, in order to address inequality and the interconnected sustainability problems facing the world. The scientific community often points a finger at the failure of governments to address these issues. The scientific community, however, also needs to take care of its responsibility and opportunities to help bridge that divide. Big-science projects have the power to make a substantial difference in this regard. 1. [↵][3]SKA Africa: Square Kilometre Array ([www.ska.ac.za][4]). [1]: pending:yes [2]: #ref-1 [3]: #xref-ref-1-1 View reference 1 in text [4]: http://www.ska.ac.za

Superbubble dynamics in globular cluster infancy

The picture of the early evolution of globular clusters has been significantly revised in recent years. Current scenarios require at least two generations of stars of which the first generation (1G), and therefore also the protocluster cloud, has been much more massive than the currently predominating second generation (2G). Fast gas expulsion is thought to unbind the majority of the 1G stars. Gas expulsion is also mandatory to remove metal-enriched supernova ejecta, which are not found in the 2G stars. It has long been thought that the supernovae themselves are the agent of the gas expulsion, based on crude energetics arguments. Here, we assume that gas expulsion happens via the formation of a superbubble, and describe the kinematics by a thin-shell model. We find that supernova- driven shells are destroyed by the Rayleigh-Taylor instability before they reach escape speed for all but perhaps the least massive and most extended clusters. More power is required to expel the gas, which might plausibly be provided by a coherent onset of accretion onto the stellar remnants. The resulting kpc-sized bubbles might be observable in Faraday rotation maps with the planned Square Kilometre Array radio telescope against polarised background radio lobes if a globular cluster would happen to form in front of such a radio lobe.

Telescope Project Splits Array to Avoid Division

The member states of the Square Kilometre Array radio telescope have decided to split the €1.5 billion project between the two potential hosts: South Africa and Australia/New Zealand.

A Technique for Differential Noise Figure Measurement of Differential LNAs

This paper presents an approach to measure the noise figure of a differential low-noise amplifier (LNA) based on familiar ldquocold-hotrdquo single-ended noise figure measurements. To demonstrate the usefulness of this approach, measurement results are presented for a wideband differential LNA designed to be used as the first stage of the receiver in the Square Kilometre Array radio telescope. The presented LNA achieves less than 0.41 dB of differential noise figure in the 700 MHz to 1.4 GHz band, differential S11 <-13 dB, differential S21 between 18 and 14 dB, single-ended output P1 dB of -8.2 dBm, and output IP3 of -1 dBm while consuming 81 mA from a 1.3-V supply. The approach of measuring the differential noise figure may be automated with one switch at the output of a standard noise source and one switch at the input to a standard noise figure analyzer or a noise figure meter, allowing for automated noise figure measurements of differential LNAs based on the differential pair topology.

Summary of the ‘Sub-microJansky Radio Sky’ Workshop

AbstractThe Square Kilometre Array Radio Telescope is the next generation radio telescope. An international project is currently under way to design and build an instrument having an effective collecting area two orders of magnitude greater than that of any existing telescope. A number of separate studies are presently investigating how to design the Square Kilometre Array to best carry out the kinds of observations desired by the astronomical community. We present a summary of one of these studies, a workshop called The ‘Sub-microJansky Radio Sky’ held at the ATNF, Sydney, on 17 June 1998. This workshop addressed the nature of the radio sky at the very faint flux densities likely to be attainable by the Square Kilometre Array. In particular, each speaker investigated a separate population of radio sources and how the expected appearance of that population at such faint flux densities would dictate how to refine some of the design constraints for the Square Kilometre Array.