New Details Shed Light On Galaxy Evolution
October 22, 2012

New Details Shed Light On Galaxy Evolution

[WATCH VIDEO: Computer Model Shows a Disk Galaxy´s Life History]

Lee Rannals for — Your Universe Online

After a comprehensive study of hundreds of galaxies, astronomers have uncovered a surprising trend in galaxy evolution.

The team studied a sample of 544 blue galaxies from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, and wrote about their findings in The Astrophysical Journal.

"Astronomers thought disk galaxies in the nearby universe had settled into their present form by about 8 billion years ago, with little additional development since," Susan Kassin, an astronomer at NASA's Goddard Space Flight Center in Greenbelt, Md. and the study's lead researcher, said in a press release. "The trend we've observed instead shows the opposite, that galaxies were steadily changing over this time period."

Star-forming galaxies take the form of disk-shaped systems like the Andromeda Galaxy or the Milky Way, where rotation dominates over other internal motions.

The most distant blue galaxies in the study were very different, exhibiting disorganized motions in multiple directions. There is a steady shift toward greater organization to the present time as the disorganized motions dissipate and rotation speeds increase.

Blue galaxies show less disorganized motions and ever-faster rotation speeds the closer they are observed to present day. This trend also holds true for galaxies of all masses.

The team said that the distant galaxies they studied are gradually transforming into rotation disk galaxies like the Milky Way.

"Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today," co-author Benjamin Weiner, an astronomer at the University of Arizona in Tucson, said in the press release. "By neglecting them, these studies examined only those rare galaxies in the distant universe that are well-behaved and concluded that galaxies didn't change."

The researchers looked at all galaxies with emission lines bright enough to be used for determining internal motions. These lines are the discrete wavelengths of radiation characteristically emitted by the gas within a galaxy.

The lines are revealed when a galaxy's light is separated into its component colors, and are able to carry information about the galaxy's internal motions and distance.

The researchers say the Milky Way must have gone through the same rough-and-tumble evolution as the galaxies in the DEEP2 sample, but gradually settled into its current state.

In the past eight billion years, the numbers of mergers between galaxies large and small has decreased sharply, as well as the overall rate of star formation and disruptions of supernova explosions.

Scientists believe that these factors play a role in creating the evolutionary trend seen in the galaxies.

Astronomers will be able to take this research into account and adjust computer simulations of galaxy evolution, which could guide scientists to the physical processes responsible.