Galactic Raw Material Plays Crucial Role In Star Formation
June 25, 2013

Galactic Raw Material Plays Crucial Role In Star Formation

Lawrence LeBlond for - Your Universe Online

New observation using an Australian telescope has offered up evidence of the raw material that played a part in forming some of the first stars in galaxies when the Universe was just three billion years old.

The observations were made using CSIRO’s Australia Telescope Compact Array (ATCA) near Narrabri, New South Wales.

“[This is] one of very few telescopes in the world that can do such difficult work, because it is both extremely sensitive and can receive radio waves of the right wavelengths,” said CSIRO astronomer Professor Ron Ekers.

However, the raw material responsible for making these stars, cold molecular hydrogen gas (H2), cannot be detected directly. To determine its presence, the telescope picks up the signature ‘tracer’ gas carbon monoxide (CO), which emits radio waves.

Since ATCA can detect star formation, hence being able to answer fundamental questions about how early galaxies started forming stars, astronomers led by Dr. Bjorn Emonts of CSIRO Astronomy and Space Science utilized the telescope to study a massive, distant group of star-forming clumps (protogalaxies) that are in the process of forming a single massive galaxy.

Called the Spiderweb, this cluster of proto-galaxies lies more than ten thousand million light-years away and  is comprised of at least sixty thousand million times the mass of the sun in molecular hydrogen gas, spread over a distance of nearly 250,000 light-years.

Dr. Emonts and his team believe this must be the fuel for star-formation that has been observed across the Spiderweb. "Indeed, it is enough to keep stars forming for at least another 40 million years," Dr. Emonts noted.

Dr. Manuel Aravena of the European Southern Observatory (ESO) and his colleagues conducted separate studies on two very distant galaxies and also found presence of CO, and therefore H2.

Dr. Aravena explained faint radio waves from these distant galaxies were amplified by the gravitational fields of other galaxies – ones that lie between us and them. This gravitational lensing “acts like a magnifying lens and allows us to see even more distant objects than the Spiderweb," he said.

By using the radio emission given off by the galaxies, Dr. Aravena and his team were able to measure the amount of H2 in each. In galaxy SPT-S 053816-5030.8, they were able to further use the radio emission to make an accurate estimate of how rapidly the galaxy is forming stars. Dr. Aravena noted this method is independent of other methods astronomers have used to measure the rate of star formation.

Ekers noted ATCA’s ability to detect CO comes thanks to an upgrade that has boosted its bandwidth sixteen-fold (from 256 MHz to 4 GHz). This process has made the telescope array far more sensitive in picking up as much of the radio spectrum at any one time as possible.

"The Compact Array complements the new ALMA telescope in Chile, which looks for the higher-frequency transitions of CO," he said.


Image Below (Left): In blue, the carbon monoxide gas detected in and around the Spiderweb. Credit: B. Emonts et al (CSIRO/ATCA)

Image Below (Right): The Spiderweb, imaged by the Hubble Space Telescope – a central galaxy (MRC 1138-262) surrounded by hundreds of other star-forming 'clumps'. Credit: NASA, ESA, George Miley and Roderik Overzier (Leiden Observatory)