Intergalactic space is much more crowded than people might think. Between the galaxies, in what might appear an endless void, there are gas clouds that have remained unchanged almost since the Big Bang. We knew they were everywhere, but now we know how big they are.
Jeffrey Cooke of the Swinburne University of Technology and John O’Meara of St. Michael’s College presented a new technique for determining the size of these giant gas clouds at the 227th meeting of the American Astronomical Society in Florida this week.
These gas clouds are called damped Lyman alpha systems (DLAs) because they absorb a very specific wavelength of light called Lyman alpha. They were discovered in 1970 by astronomer Roger Lynds: He saw that the Lyman alpha emission from a quasar was absorbed, indicating that in its path from the galaxy to us it had encountered several cool clouds. The clouds are very cold and emit a small amount of radiation, so it has been very difficult to learn about their nature.
All the information we had on these clouds was indirect; they needed to be illuminated from behind for us to spot them. The traditional method uses quasars, but they are relatively small and rare to be used to understand the wider properties of these clouds.
The new technique employs galaxies that are common and increase the observable area 100 million times. “Using the galaxy technique, DLAs can be studied in large numbers to provide a 3-D tomographic picture of the distribution of gas clouds in the early universe and help complete our understanding of how galaxies formed and evolved over cosmic time,” says O’Meara in a statement.
Artist's impression of the power of background galaxies to measure the size of gas clouds, compared to the conventional method of using quasars. Adrian Malec and Marie Martig
The investigation has highlighted that the clouds are huge. The size combined with the composition makes the clouds the potential birthplace of the galaxies we see today. All the results were accepted for publication in the Astrophysical Journal Letters, and the paper is available on ArXiv.
The method is not without flaws, though. To detect the DLAs, it is necessary to produce long and deep exposures, which were provided by some of the most powerful telescopes in the world. Future observation campaigns will be able to study DLAs in larger numbers.
“The technique is timely as the next generation of giant 30-meter telescopes will be online in several years and are ideal to exploit this method to routinely gather large numbers of DLAs for study,” Cooke added.