Scientists use the galaxy as a ‘cosmic telescope’ to study the core of the young universe

A unique new instrument, combined with a powerful telescope and a little help from nature, has given scientists the opportunity to look into galactic nurseries in the heart of the young universe.

After the big bang about 13.8 billion years ago, the early universe was filled with huge clouds of diffuse neutral gas, known as Damped Lyman-α or DLA systems. These DLAs served as galactic nurseries as the gases inside slowly condensed to nourish the formation of stars and galaxies. You can still see them today, but it’s not easy.

“DLAs are a key to understanding how galaxies form in the universe, but they are generally difficult to observe because the clouds are too diffuse and do not even emit light,” explains Rongmon Bordoloi, a professor of physics assistant at North Carolina State University. and corresponding author of the research.

Currently, astrophysicists use quasars – supermassive black holes that emit light – as “backlight” to detect DLA clouds. And while this method allows scientists to pinpoint DLA locations, light from quasars acts only as small spears through a massive cloud, hampering efforts to measure their overall size and mass.

But Bordoloi and John O’Meara, chief scientist at the WM Keck Observatory in Kamuela, Hawaii, found a way around the problem by using a gravitational lens galaxy and integral field spectroscopy to observe two DLAs – and the host galaxies inside – which formed approx. 11 billion years ago, shortly after the big bang.

“Gravitational-lensed galaxies refer to galaxies that appear to be stretched and illuminated,” Bordoloi explains. “It’s because there’s a massive gravitational structure in front of the galaxy that bends the light that comes from it when it’s on its way to us. So we end up looking at an extended version of the object – it’s like using a cosmic telescope that increases the magnification and gives us better visualization.

“The advantage of this is twofold: firstly, the background object is stretched across the sky and bright, so it is easy to take spectrum readings on different parts of the object. Secondly, because the lens expands the object, you can probe very small scales. for example, if the object is a light year in diameter, we can study small pieces with very high fidelity. ”

Spectrum readings allow astrophysicists to “see” functions in deep space that are not visible to the naked eye, such as diffuse gaseous DLAs and the potential galaxies they contain. Usually, collecting readings is a long and laborious process. However, the team solved this problem by performing integral field spectroscopy with Keck Cosmic Web Imager.

Integral field spectroscopy enabled scientists to obtain a spectrum at each pixel of the targeted part of the sky, making spectroscopy of an extended object in the sky very effective. This innovation combined with the stretched and diluted gravitational lens galaxy allowed the team to map diffuse DLA gas in the sky with high credibility. Using this method, the researchers were able to determine not only the size of the two DLAs, but also that they both contained host galaxies.

“I’ve been waiting most of my career for this combination: a sufficiently powerful telescope and instrument, and nature gives us a few lucky adjustments to study not one but two DLAs in a rich new way,” says O’Meara. “It is fantastic to see science being implemented. »

Incidentally, DLAs are huge. With diameters larger than 17.4 kiloparsecs, they are now more than two-thirds the size of the Milky Way galaxy. By comparison, a typical galaxy 13 billion years ago would be less than 5 kiloparsecs in diameter. A parsec is 3.26 light-years and a kiloparsec is 1,000 parsecs, so it would take about 56,723 light-years to pass through each DLA.

“But to me, the most amazing thing about the DLAs we observed is that they are not unique – they seem to have similarities in structure, host galaxies have been discovered in both, and their masses indicate that ‘they contain enough fuel for the next generation of star formation, ‘says Bordoloi. “With this new technology at our disposal, we will be able to dig deeper into how stars were formed in the early universe. »

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

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