A Look At The Galactic Plane With Askap (Cosmology)

Leveraging the Australian forerunner of the Ska project, the first map of a section of the Milky Way’s galactic plane (about 40 square degrees wide) was created with an angle of sensitivity and resolution never before achieved by an infrastructure in the southern hemisphere. The results were published in Mnras by a group of radio astronomers led by INAF and the University of Macquarie in Sydney.

A group of radio astronomers, led by the National Institute of Astrophysics (INAF) and the University of Macquarie in Sydney, made the first radio observations of a large section of the galactic plane of the Milky Way with the Australian Ska Pathfinder (Askap) , developed and managed by the Commonwealth Scientific and Industrial Research Organization (Csiro). Specifically, the region mapped by the researchers includes the entire area of ​​the Scorpio survey (Stellar Continuum Originating from Radio Physics In Ourgalaxy), one of the numerous exploration projects of the broader Evolutionary Map of the Universe (Emu) program, which consists of observation of the whole southern hemisphere with Askap, one of theprecursors of the Ska project . The observations, reported in two articles published in the Monthly Notices of the Royal Astronomical Society , were made in 2018 with the interferometer not yet fully deployed (15 of the 36 antennas were operational at the time), covering a total area of ​​about 40 degrees squares. 

As part of the preparatory activities for the EMU survey , Askap’s antennas were pointed towards the tail of the constellation of Scorpio. The so-called Scorpio field was included among the first targetsscientific studies of Askap, thanks to the preliminary work carried out by the Italian team of INAF using the Australia Telescope Compact Array (Atca), which allowed to achieve a series of important scientific results and to develop skills in the reduction and analysis of radio data of the plan galactic. More than 3,600 compact radio sources have been extracted from the Scorpio field, many of which are unclassified. All the sources previously classified as HII regions, areas rich in ionized hydrogen associated with star formation sites, or as planetary nebulae, the last evolutionary phases of stars of intermediate mass, have been revealed and new ones have been discovered, significantly increasing the number of objects belonging to these different galactic populations.radio quiet and to discover numerous extended sources, not classified and belonging to the class of so-called “galactic bubbles”, which constitute a new sample within which to identify new supernova remains. 

Composite image of a portion of the Scorpio field. In green the infrared data collected by Spitzer / Glimpse, in red those collected by Herschel / Hi-Gal and in blue the radio data collected by Askap. By superimposing infrared data (which track dust) on radio maps (which track either ionized gas or synchrotron), radio and infrared coincide in star-forming regions, while in the case of supernova remnants (Snr) only radium is visible . Credits: G. Umana / Inaf

“Scorpio is the only galactic field observed so far with Askap and is therefore particularly important for the characterization of some galactic populations”, explains Grazia Umana , principal investigator of the survey and first author of one of the two articles, as well as a researcher at INAF of Catania, «because it provides a solid base level from which to start to better design some aspects of the EMU survey . In addition to the discovery of numerous galactic radio sources, these observations have highlighted Askap’s unique feature of mapping complex objects at various angular scales, an extremely useful feature especially in the case of studies of the galactic plane. This is the result of a skilful design byarray that is sensitive to both compact objects and extended and diffuse emission. On the basis of these first results of observations of the galactic plane with Askap we can have only a small taste of the potential of the Ska project in the field of galactic radio astronomy ». 

The galactic plane is the place in the Milky Way where the solar system resides: it contains countless stars, dust and gas clouds, as well as a significant amount of dark matter. Studying the plan of the Milky Way has always been one of the most important objectives of radio astronomers, but the presence of diffuse emission in the galaxy makes it difficult to obtain artifact-free images: this effectively reduces the quality of the final images making data analysis a task. particularly challenging. Many of these problems have been mitigated using different approaches and increasingly complex algorithms, but due to the large amount of data provided by tools such as Askap, human intervention at each stage of data reduction is not possible and this requires a different approach. .

” Numerous difficulties have arisen in the data reduction phase”, underlines Simone Riggi , researcher at INAF in Catania and first author of the survey catalog article , “because the standard techniques are currently optimized for extragalactic fields in which the emission diffuse that permeates the galactic plane is not present. It was therefore necessary to develop new procedures for data calibration and define new strategies in the data acquisition phase. What we have learned will allow us to contribute to the design of the EMU survey , optimizing its scientific return also for galactic science.An important part of the work done with the Ska precursors is to gain experience in managing the representative data of the Ska project. A significant challenge with these huge datasets, beyond data reduction itself, is to automatically find and classify radio sources. ‘ 

The Milky Way extending over the Askap radio telescope operated by Csiro (the Australian Scientific Agency) at the Murchison Radio-astronomy Observatory in Western Australia. Askap is one of the forerunners of the Ska project. Credits: Csiro / A. Cherney

The Scorpio field was used as a test bench to test the Caesar source extraction tool developed by the Italian team on real data and in the presence of diffuse emission . A first catalog of compact radio sources and their components was produced, which will be subsequently updated when the new Askap observations of the Scorpio field with the complete array are available, scheduled for the end of 2021. “Multi-frequency data and the expected increase in sensitivity and spatial resolution will allow us to measure the spectral index for all sources, enabling further progress in our classification studies, ”adds Riggi.

“The data collected at that early stage of Askap also demonstrates its excellent sensitivity to extended radio emissions,” says Andrew Hopkins , head of the EMU project for Macquarie University. «A fundamental result to allow us to detect these important structures in the Milky Way, allowing us to deepen our knowledge on the formation and evolution of stars in the galaxy».

The EMU project will also extend to part of the northern hemisphere, covering 75 percent of the sky observed at the 1.4 GHz frequency, with better angular resolution and sensitivity than achieved so far. The researchers will observe a large fraction of the galactic plane and will be able to produce a wide-field atlas of the Milky Way’s continuous radio emission, with unprecedented results in terms of sensitivity and angular resolution, which will have a major impact in star formation studies. of the galactic structure and stellar evolution.

«New Askap observations of the galactic plane as part of the EMU survey and subsequently with the Ska project will allow us to explore a whole series of observational parameters with a very high probability of discovering new classes of objects. Our final goal is to acquire and consolidate the skills and competences in view of the development of the entire antenna array of the Ska project, in order to be ready and competitive to lead and participate in the Ska Key Science Projects (Ksp) and to full exploitation of data », Umana concludes.

Featured image: Askap image of the Scorpio field at 912 MHz. The mosaic covers a region of approximately 40 square degrees. The shape of the galactic equator is defined by a series of compact sources and regions of ionized hydrogen (H II regions), associated with star formation sites. Several supernova remnants (Snr) are also visible. Outside the galactic plane some large and bright structures are evident. Among these, the region in the upper center of the field includes the regions H II G345.45 + 1.50 and IC 4628. The white frames are zoom of some representative objects, clockwise, a Snr, a star-forming region with a Massive Young stellar Object, another star-forming region and a pair of Snr. Credits: G. Umana / Inaf

To know more:

  • Read on  Monthly Notices of the Royal Astronomical Society the article ” A first glimpse at the Galactic Plane with the ASKAP: the SCORPIO field “, by G. Umana, C. Trigilio, A. Ingallinera, S. Riggi, F. Cavallaro, J. Marvil, RP Norris, AM Hopkins, CS Buemi, F. Bufano, P. Leto, S. Loru, C. Bordiu, JD Bunton, JD Collier, M. Filipovic, TMO Franzen, MA Thompson, H. Andernach, E . Carretti, S. Dai, A. Kapinska, BS Koribalski, R. Kothes, D. Leahy, D. Mcconnell, N. Tothill and MJ Michałowski
  • Read on  Monthly Notices of the Royal Astronomical Society the article ” Evolutionary map of the Universe (EMU): Compact radio sources in the SCORPIO field towards the galactic plane “, by S Riggi, G Umana, C Trigilio, F Cavallaro, A Ingallinera , P Leto, F Bufano, RP Norris, AM Hopkins, MD Filipović, H Andernach, J Th van Loon, MJ Michałowski, C Bordiu, T An, C Buemi, E Carretti, JD Collier, T Joseph, BS Koribalski, R Kothes , S Loru, D McConnell, M Pommier, E Sciacca, F Schillirò, F Vitello, K Warhurst and M Whiting,
  • Askap is a network of radio telescopes located at the Murchison Radio Astronomy Observatory in the desert region of Western Australia, where the Aboriginal Wajarri Yamatji ethnic group has resided for millennia. Managed and operated by the Australian scientific agency Csiro, Askap has 36 parabolic antennas of 12 meters in diameter with a collection area of ​​4000 square meters: each of the antennas required 13 to 18 hours of assembly. Thirty antennas are arranged in a circle of 2 kilometers in diameter, while the remaining 6 antennas are arranged to form a Reuleaux triangle with a maximum distance from the center of 6 kilometers. Askap is one of the forerunners of the SKA project and has been operational since 2012, but official scientific observations began only from 2020.

Provided by INAF

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