16 January 2022

Led by INAF and Macquarie University, a portion of our Galaxy has been imaged in great detail as part of the PEGASUS survey - a radio astronomy project designed to discover more about the Milky Way.

Radio observations of a large section of the Galactic plane of the Milky Way were conducted with the ASKAP radio telescope and the Parkes radio telescope, Murriyang, both developed and managed by Australia’s national science agency, CSIRO. A group of radio astronomers, led by the National Institute of Astrophysics (INAF), used Parkes to "photograph" a large portion of the disk of our Galaxy, about 6-7 degrees or 12-14 full moons in length, within the PEGASUS survey. This image was combined with one produced with ASKAP for the EMU project led by Australia’s Macquarie University, obtaining an image of stunning quality.

This work is in preparation for the PEGASUS survey. In addition, PEGASUS will support the research of three large scientific consortia, EMU and POSSUM (two ASKAP projects) and GMIMS.

PEGASUS is one of the numerous exploration projects of the broader EMU program. EMU was created to observe the southern hemisphere with ASKAP, a precursor telescope to the international SKA project. The image shows a region featuring extended emission associated with hydrogen gas filling the space between the stars, dying stars called supernova remnants, and hot bubbles of ionised hydrogen gas related to the birth of new stars. The stars themselves are not visible, as starlight contains minimal radio emission. This view of our Galaxy shows details of the birth and deaths of stars only visible to radio telescopes.

POSSUM works hand-in-hand with EMU, capturing the polarised radio signal, aiming to measure about one million radio objects. The data will help map magnetic forces within our Milky Way and enable studies of the history of magnetic forces in the Universe. POSSUM data will also portray fine details of the emission from the Milky Way.

Ettore Carretti, from INAF, is the leader of the PEGASUS project along with Tom Landecker from the National Research Council of Canada (NRC) and Xiaohui Sun from Yunnan University, China. PEGASUS aims to use Parkes to map the entire Southern sky at 700-1440 MHz with about 2100 hours of observation. The PEGASUS project has just completed its pilot observations and aims to observe the entire southern sky in the next two years.

The radio astronomer from INAF explains: “With the pilot phase of PEGASUS, we studied a large region of the Galactic plane of our Galaxy, full of supernova remnants, regions of ionising hydrogen and planetary nebulae, which, thanks to the combination of data from ASKAP and Parkes, can be studied with extremely high precision. When our Canadian colleague, Dr. Roland Kothes, NRC, combined the PEGASUS map with that from the EMU and POSSUM observations, the result was marvelous; when we opened the image for the first time, we were amazed by such quality and beauty.”

Carretti adds: "The goal for this survey is two-folded. First, to understand the magnetic fields of our Galaxy, their origin and their effects on various phenomena such as supernova remnants and the large structures of the Milky Way, such as the North Polar Spur, and to study galaxies, radio galaxies and galaxy clusters. Second, ASKAP, like other interferometers, is not sensitive to large angular scales. Therefore, PEGASUS’ data collected with Parkes will complement ASKAP data, adding to the already existing fine details the complete shape, size and total power emitted by these objects. With the combined data, we can study the physics of the phenomena that drives them."

Tom Landecker explains: “Our GMIMS project, the Global Magneto-Ionic Medium Survey, is an exploration of magnetic forces in the Milky Way. In addition to shaping the Milky Way, magnetic forces are involved in its life, from the formation of its spiral structure to the births and deaths of stars within its spiral arms. Our primary data are observations of the polarization of radio emission from the Milky Way made with large radio telescopes in the Southern and Northern hemispheres. Over 12 years we have made successful surveys of the sky with the Parkes Murriyang telescope at lower and higher radio frequencies. PEGASUS will now fill a gap in our data, providing an unprecedented view of magnetic effects in 3 dimensions. Parallel observations have been made in the North, using Canadian telescopes, and more are underway, providing a truly global outlook.”

Surveys like PEGASUS observe the entire sky, including the Galactic plane. The Galactic Plane is where the Solar System resides: it contains numerous stars, dust, and gas clouds, as well as a significant amount of dark matter. Studying the equator of the Milky Way has always been an essential objective for radio astronomers. However, the Galaxy's diffuse emission makes obtaining artefact-free images challenging.

The quality of the image of this first observation is superb. The leader of the EMU project, Andrew Hopkins of Macquarie University, explains: “The eventual results will be an unprecedented view of almost the entire Milky Way, about a hundred times larger than this initial image, but achieving the same level of detail and sensitivity.”

PEGASUS will observe the entire sky. Besides the Milky Way,  the combination with EMU and POSSUM also promises to obtain images of impressive quality for extragalactic objects such as galaxies and clusters of galaxies.

More information:

ASKAP and Parkes are owned and operated by CSIRO, Australia’s national science agency, as part of the Australia Telescope National Facility. CSIRO acknowledge the Wajarri Yamatji people as the Traditional Owners and native title holders of Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory, where ASKAP is located, and the Wiradjuri people as the traditional owners of the Parkes Observatory.

Contacts:

●      INAF Press Office - Marco Galliani: +39 335 1778428, ufficiostampa@inaf.it

●      CSIRO, Australia’s national science agency - Rachel Rayner, +61 2 9372 4172, rachel.rayner@csiro.au

●      Macquarie University - Megan Hoole, +61 2 9850 7615, megan.hoole@mq.edu.au