Remote Galaxies Grew Gradually by Grazing Gas

Galaxies in the early universe fed slowly on gas, rather than ingesting quick bursts after collisions with other galaxies, according to new research based on infrared data from NASA’s Spitzer Space Telescope.

Previously, scientists believed early galaxies acquired their star-forming fuel from gas stirred up in intergalactic collisions.

Ranga-Ram Chary at NASA’s Spitzer Science Center (SSC) at the California Institute of Technology and colleagues surveyed more than 70 remote galaxies from one to two billion years after the Big Bang. The team found high levels of H alpha radiation from hydrogen gas that has been blasted with ultraviolet starlight, indicating vigorous star formation.

“Our study shows the merging of massive galaxies was not the dominant method of galaxy growth in the distant universe,” said Ranga-Ram Chary of NASA’s Spitzer Science Center (SSC) at the California Institute of Technology, in a press release.

“We’re finding this type of galactic cannibalism was rare,” he added. “Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought.”

These galaxies fed gradually, over hundreds of millions of years, yet forming stars up to 100 times faster than the current rate of our Milky Way, and up to 100 times the mass of the sun.

“This is the first time that we have identified galaxies that supersized themselves by grazing,” said lead author Hyunjin Shim, also at SSC, in the release. “They have many more massive stars than our Milky Way galaxy.”

Even though galactic collisions are common, the scientists found that early galaxies mostly grew by grazing on a steady supply of gas, which they believe streamed in from filaments of dark matter.

Seventy percent of the remote galaxies showed high levels of H alpha compared with only 0.1 percent of galaxies in our local universe.

Chary concluded: “If you could visit a planet in one of these galaxies, the sky would be a crazy place, with tons of bright stars, and fairly frequent supernova explosions.”

The paper will appear in the Aug. 1 issue of the Astrophysical Journal.