Cosmic telescope reveals inner workings of two proto-galaxies

Using a unique new instrument and a little help from nature, Swinburne researchers have obtained the first in-depth view of the vast clouds of gas that serve as galactic nurseries.

Working internationally with researchers from North Carolina State University and the WM Keck Observatory, astronomers have first observed the formative inner workings of two Damped Lyman-α systems (DLAs). DLAs are giant clouds of gas that formed galaxies in the early Universe, not long after the Big Bang.

“DLAs are crucial to understanding how galaxies formed, but have historically been extremely difficult to observe,” said Professor Jeff Cooke of Swinburne University of Technology, one of the authors of the recently published paper in Nature.

“By leveraging the powerful capabilities of the WM Keck Observatory, some random alignments of galaxies, and Einstein’s general theory of relativity, we are able to observe and study these hugely important objects in a whole new way, giving us insight get into how the stars and planets around us are formed.”

Not only are these DLAs hugely important; they are also huge, as this study shows. At more than 17.4 kiloparsecs in diameter, they are more than two-thirds the size of the current Milky Way Galaxy. It would take light over 50,000 years to travel through each of them.

Developing a cosmic telescope

After the Big Bang, DLAs served as galactic nurseries and fueled the formation of galaxies made up of stars and gas. But it was difficult to observe them because they are mainly made of hydrogen, which does not shine or glow.

Astrophysicists have traditionally used bright quasars — supermassive black holes that emit light — as backlighting to search for DLAs. While this method allows researchers to find DLAs, the light from a quasar only provides a small skewer through the huge cloud, like a pinprick poked into a sheet of paper.

“Background” galaxies can provide very large backlighting for observation, as they are 100 million times larger than quasars in this context. However, galaxies are usually too dim for this purpose.

dr. Rongmon Bordoloi of North Carolina State University and John O’Meara, chief scientist at the WM Keck Observatory in Hawaii, in collaboration with Professor Cooke of Swinburne, have found a way around the problem by using a gravitational lens galaxy and integral field spectroscopy.

A Hubble Space Telescope image of the galaxy examined in this work. Provided: Professor Jeff Cooke.

“Gravity-lensing galaxies refer to galaxies that appear stretched and brighter,” says Dr. bordoloi. “The light bends as it travels toward us, so we end up looking at an expanded version of the object — it’s like using a cosmic telescope that increases the magnification and gives us better visualization.”

The bending and magnification of the galaxy light is due to general relativity.

Innovative spectrum measurements

Spectrum measurements allow astrophysicists to “see” elements in deep space from their atomic signatures that are not visible in images. This helps understand the magnitude of the gas, its movement and the elemental composition of the DLAs.

Normally, collecting the measured values ​​is a long and tedious process. But the team solved the problem by performing integral field spectroscopy with the Keck Cosmic Web Imager, which can simultaneously collect spectra across many parts of the DLAs.

This innovation, combined with the stretched and brightened gravitational lensing background galaxy, allowed the team to map the diffuse gas in the two DLAs in high fidelity.

“By taking advantage of the latest technology at Keck and a little luck with the alignment of galaxies with gravitational lenses, we have more insight into the workings of our universe than ever before,” said Professor Cooke.

Swinburne is the only Australian university with guaranteed access to WM Keck Observatory telescopes – the world’s largest and most productive optical/infrared telescopes – located more than 9,000 kilometers from Melbourne.

The work appears in Nature and was supported by the National Aeronautics and Space Administration, the WM Keck Foundation, the National Science Foundation and the Australian Research Council Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).

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