A unique new instrument, combined with a powerful telescope and a little help from nature, has given researchers the ability to peer into galactic nurseries at 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 within slowly condensed to fuel 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 emit light themselves,” explains Rongmon Bordoloi, professor Physics Assistant at North Carolina State University. and corresponding author of the research.
Currently, astrophysicists use quasars – supermassive black holes that emit light – as “backlights” to detect DLA clouds. And while this method allows researchers to pinpoint DLA locations, light from quasars only acts like small skewers through a massive cloud, hampering efforts to measure their total 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 gravitationally lensed galaxy and integral field spectroscopy to observe two DLAs – and the host galaxies inside – which formed around 11 billion years ago, shortly after the Big Bang.
“Gravitational lensed galaxies refer to galaxies that appear stretched out and lit up,” Bordoloi explains. “That’s because there’s a massive gravitational structure in front of the galaxy that bends the light coming from it as it heads towards us. So we end up looking at an extended version of the object – it’s like using a cosmic telescope that increases magnification and gives us better visualization.
“The advantage of this is twofold: First, the background object is extended across the sky and bright, so it’s easy to take spectrum readings on different parts of the object. Second, because the lens extends 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” features in deep space that are not visible to the naked eye, such as diffuse gaseous DLAs and the potential galaxies within them. Normally, collecting readings is a long and laborious process. But the team solved this problem by performing integral field spectroscopy with the Keck Cosmic Web Imager.
Integral field spectroscopy allowed the researchers to obtain a spectrum at each pixel of the targeted part of the sky, making spectroscopy of an extended object in the sky very efficient. This innovation combined with the stretched and thinned gravitationally lensed galaxy allowed the team to map diffuse DLA gas in the sky with high fidelity. 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 waited most of my career for this combination: a sufficiently powerful telescope and instrument, and nature giving us a few lucky alignments to study not one but two DLAs in a rich new way,” says O’Meara. “It’s great to see the science come to fruition.”
DLAs are huge, by the way. With diameters greater than 17.4 kiloparsecs, they are now more than two-thirds the size of the Milky Way galaxy. For comparison, 13 billion years ago, a typical galaxy 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 detected 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’re going to be able to dig deeper into how stars formed in the early universe.”
The book appears in the journal Nature.
New method solves 40-year-old mystery about the size of dark galaxies
Rongmon Bordoloi, Solving HI in Damped Lyman-α Systems That Power Star Formation, Nature (2022). DOI: 10.1038/s41586-022-04616-1. www.nature.com/articles/s41586-022-04616-1
Provided by North Carolina State University
Quote: Researchers use the galaxy as a “cosmic telescope” to study the heart of the young universe (May 18, 2022) retrieved on May 19, 2022 from https://phys.org/news/2022-05-galaxy-cosmic-telescope-heart – young.html
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