Prof. Rachel Webster

Research Interests

Gravitational Lensing | Quasars | Large HI Surveys

Professor Rachel Webster's research career began at Cambridge University under the supervision of eminent astronomer, Lord Martin Rees. Her PhD research on Gravitational Lensing and Cosmology, marked the beginning of her illustrious career as an observational astrophysicist and cosmologist. Following her studies at Cambridge, Professor Webster moved to the University of Toronto to take up a postdoctoral position at the Canadian Institute for Theoretical Astrophysics. Her research focussed on the modelling and interpretation of light curves from the gravitationally lensed quasar, Q2237+0305 (also known as the Einstein Cross).

In 1992, she returned to the University of Melbourne where she began working on the Parkes Quasar Survey. This research focussed on the identification of a complete sample of flat spectrum radio sources using imaging and spectroscopy in the near infra-red (NIR), to search for high red-shift quasars. This lead to the first detailed investigations of dust-obscured quasars; the obscuring dust being either extrinsic (in the line-of-sight), or intrinsic to the region of the quasar itself. Her team found evidence for a large undetected population of dust reddened quasars, demonstrating that up to 80% of quasars may be missed in traditional optical surveys. Professor Webster was also one of the lead investigators of the HI Parkes All Sky Survey (HIPASS), and ambitious 5+ year survey that mapped the southern sky at radio wavelengths, to map the neutral hydrogen (HI) content in, and around galaxies.

Today, her research focusses on understanding the emission mechanism of quasars, further gravitational lensing studies, and research towards understanding the Epoch of Reionization (EoR). The EOR is an early period in the history of the universe during which the predominantly neutral intergalactic medium (IGM) was ionized following the emergence of the first luminous sources. Identifying these sources is a primary goal and the focus of her scientific research within the Murchison Widefield Array (MWA) collaboration. While the MWA does not currently have sufficient sensitivity to directly image individual features in the EOR signal, it serves as a critical test–bed for similar experiments that will be achievable with the future Square Kilometre Array (SKA).

In addition to Australian and international radio telescopes, Professor Webster's research also exploits the world-class Gemini telescopes in Hawaii and Chile, the Hubble Space Telescope (HST), and the Chandra X-Ray Observatory.

Research Supervision

The Masters of Science in Physics (Astrophysics) comprises both coursework and research. The Doctor of Philosophy and Master of Philosophy comprises a research projects. Research projects offered by Professor Rachel Webster include the following topics;

• Epoch of Reionisation
• Galaxy formation
• Large-scale structure and cosmology
• Quasar astrophysics

Scientific Collaborations

Recent Publications

PUMA: The Positional Update and Matching Algorithm. Publications of the Astronomical Society of Australia 34. (2017)
Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies. Astrophysical Journal. 838. (2017)
A high reliability survey of discrete Epoch of Reionization foreground sources in the MWA EoR0 field. Monthly Notices of the Royal Astronomical Society. 461. (2016)
CHIPS: The Cosmological HI POWER SPECTRUM ESTIMATOR. Astrophysical Journal. 818. 2016

NASA/ADS arXiv

Recent Grants

ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions – Co–I: ARC CoE (2017)
Expanding Our View of the Universe with the Murchison Wide-Field Array – Co–I: ARC LIEF (2016)
Mapping quasars: micro-imaging experiments – PI: ARC Discovery Project (2015 – 2018)
The Australia European Southern Observatory Positioner (AESOP) – Co–I: ARC LIEF (2015 – 2016)
Mapping the Dark Matter with Early–Type Galaxies – ARC Linkage Projects (2014)
Mapping the Universe with the Skymapper Telescope – ARC LIEF (2013 – 2015)

Featured Projects & Collaborations

Science | Instrumention | National Programs

ARC Centre of Excellence for All-Sky Astrophysics

By answering fundamental questions about the nature of the Universe, by developing innovative ways of processing enormous data-sets, and by providing a diverse set of opportunities for students and young researchers, CAASTRO aims to establish Australia as the world-leader in wide-field astronomy.

Murchison Wide-Field Array (MWA)

The Murchison Widefield Array (MWA) is a low-frequency radio telescope operating between 80 and 300 MHz. It is located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, the planned site of the future Square Kilometre Array (SKA) lowband telescope.

GLEAM GaLactic and Extragalactic All-sky MWA Survey

GLEAM is a large-scale, high-resolution survey of the radio sky observed at frequencies from 70 to 230 MHz, observing radio waves that have been travelling through space—some for billions of years.

KOALA – Kilofibre Optical AAT Lenslet Array

KOALA, the Kilofibre Optical AAT Lenslet Array, is a wide-field, high efficiency, integral-field unit designed for use with the bench mounted AAOmega spectrograph on the Anglo Australian Telescope (AAT).

HIPASS – HI Parkes All Sky Survey

The HI Parkes All Sky Survey (HIPASS) was an extragalactic neutral atomic hydrogen (HI) survey of the southern sky. The data was taken between 1997 and 2002 using the multibeam receiver on the 64m Parkes Radio Telescope – the most efficient detector of its time. HIPASS covered 71% of the sky and identified more than 5000 galaxies; the data led to a suite of comprehensive HI galaxy catalogues containing over 5000 galaxies. Discoveries included the Leading Arm of the Magellanic Stream.