A team of astronomers in Hawaii have discovered a new way to unlock the mysteries of how the first galaxies formed and evolved into what they are today.
For the very first time, the research team - led by Dawn Erb of the University of Wisconsin-Milwaukee - used new capabilities at W. M. Keck Observatory to examine a small, young galaxy located about 10 billion light-years away from Earth called Q2343-BX418.
In a study, published in Astrophysical Journal Letters, the astronomers found the distant galaxy is an analogue for younger galaxies that are too faint to study in detail, making it the perfect candidate for learning more about what galaxies looked like shortly after the birth of the universe. It's also renowned for its halo of gas that circles it and gives off a special type of light.
"In the last several years, we've learned that the gaseous halos surrounding galaxies glow with a particular ultraviolet wavelength called Lyman alpha emission," explained Erb.
"There are a lot of different theories about what produces this Lyman alpha emission in the halos of galaxies, but at least some of it is probably due to light that is originally produced by star formation in the galaxy being absorbed and re-emitted by gas in the halo."
The team used one of the observatory's newest instruments, something called the Keck Cosmic Web Imager (KCWI), to perform a detailed spectral analysis of BX418's gas halo; its properties could offer clues about the stars forming within the galaxy.
"Most of the ordinary matter in the universe isn't in the form of a star or a planet, but gas. And most of that gas exists not in galaxies, but around and between them," said Erb.
The halo is where gas enters and exits the system. The gas surrounding galaxies can fuel them; gas from within a galaxy can also escape into the halo. This inflow and outflow of gas influences the fate of stars.
"The inflow of new gas accreting into a galaxy provides fuel for new star formation, while outflows of gas limit a galaxy's ability to form stars by removing gas," Erb added.
"So, understanding the complex interactions happening in this gaseous halo is key to finding out how galaxies form stars and evolve."
The power of KCWI, combined with the Keck telescopes' location in Hawaii (where viewing conditions are some of the best on Earth), provided some of the most detailed glimpses of the cosmos.
Erb's team used KCWI to take spectra of the Lyman alpha emission of BX418's halo. This allowed them to trace the gas, plot its velocity and spatial extent, then create a 3-D map showing the structure of the gas and its behaviour.
Erb said this analysis is the first of its kind because it has only been tested on one galaxy. However, she said other galaxies need to be studied to see if these results are typical.
Now that the team has discovered a new way to learn about the properties of the gaseous halo, they hope to further analyse the data they collected and believe that the computer simulations modelling the processes will yield additional insights into the characteristics of the first galaxies in the universe.
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