News in Science

ALMA opens window to universe

New window on universe Distant starburst galaxies were more numerous and forming stars far earlier than previously thought, according to early observations from a revolutionary new telescope.

The findings published in the journal Nature and the Astrophysical Journal, improves sciences understanding of star formation in the early universe.

The data comes from the new Atacama Large Millimetre/sub-millimetre Array telescope (ALMA), which sees light absorbed and re-emitted by dust particles in the millimetre part of the electro-magnetic spectrum.

By looking further back through time to more distant galaxies, astronomers can determine how vigorously the universe was making stars at different stages during its 13.7 billion-year history.

Before ALMA, getting details from this early epoch has been difficult because of the immense densities of dust, making it hard to see through.

"Observing molecular emissions associated with the dusty star-forming regions of distant starburst galaxies opens a new window," says Dr Joaquin Vieira of the California Institute of Technology, and lead author of the paper.

"The average distance to these dusty starburst galaxies is significantly greater than previous estimates, with two dating back to just a billion years after the big bang," says Vieira.

"This allowed us to double the number of these starburst galaxies known as high redshift."

Redshift is a measure of how far the wavelength of the light that reaches Earth has been stretched by the expansion of the universe, allowing scientists to determine a galaxy's age and distance.

Distant galaxies

Vieira and colleagues selected 26 galaxies originally detected by the South Pole Telescope in Antarctica.

"The South Pole is more of a survey instrument, it has a low resolution, but looks at a large section of the sky," says Vieira.

"ALMA's not a survey instrument, but can instead zoom in on a particular object, providing very high resolution and sensitivity, so we can study the heck out of it."

Vieira and colleagues looked for ancient galaxies that were magnified by gravitational lensing, in which light from a background galaxy is bent and magnified by the mass of a foreground galaxy.

"These galaxies were being magnified by a factor of about 10, increasing their brightness and saving telescope time," says Vieira.

Vieira and colleagues used ALMA to obtain both an image and the spectra of each galaxy.

The images proved that these galaxies were being gravitationally lensed, and the spectra provided details about their distance and composition.

The observations show that large reservoirs of molecular gas and dust were already present early in the history of the universe.

"They have water and carbon monoxide, and it wasn't clear that these ingredients would be in place so early," says Vieira.

"It seems as soon as all the conditions are right in the universe, there's star formation taking place. I think that's pretty incredible."