Space

October 19, 2012

Astronomers uncover a surprising trend in galaxy evolution

A comprehensive study of hundreds of galaxies observed by the Keck telescopes in Hawaii and NASA’s Hubble Space Telescope has revealed an unexpected pattern of change that extends back 8 billion years, or more than half the age of the universe.

“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,” said Susan Kassin, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md., and the study’s lead researcher. “The trend we’ve observed instead shows the opposite, that galaxies were steadily changing over this time period.”

Today, star-forming galaxies take the form of orderly disk-shaped systems, such as the Andromeda Galaxy or the Milky Way, where rotation dominates over other internal motions. The most distant blue galaxies in the study tend to be 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. These galaxies are gradually settling into well-behaved disks.

Blue galaxies – their color indicates stars are forming within them – show less disorganized motions and ever-faster rotation speeds the closer they are observed to the present. This trend holds true for galaxies of all masses, but the most massive systems always show the highest level of organization.

Researchers say the distant blue galaxies they studied are gradually transforming into rotating disk galaxies like our own Milky Way.

“Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today,” said co-author Benjamin Weiner, an astronomer at the University of Arizona in Tucson. “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.”
Rather than limit their sample to certain galaxy types, the researchers instead looked at all galaxies with emission lines bright enough to be used for determining internal motions. Emission lines are the discrete wavelengths of radiation characteristically emitted by the gas within a galaxy. They are revealed when a galaxy’s light is separated into its component colors. These emission lines also carry information about the galaxy’s internal motions and distance.

The team studied a sample of 544 blue galaxies from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, a project that employs Hubble and the twin 10-meter telescopes at the W. M. Keck Observatory in Hawaii. Located between 2 billion and 8 billion light-years away, the galaxies have stellar masses ranging from about 0.3 percent to 100 percent of the mass of our home galaxy.

A paper describing these findings will be published Oct. 20 in The Astrophysical Journal.

The Milky Way galaxy must have gone through the same rough-and-tumble evolution as the galaxies in the DEEP2 sample, and gradually settled into its present state as the sun and solar system were being formed.

In the past 8 billion years, the number of mergers between galaxies large and small has decreased sharply. So has the overall rate of star formation and disruptions of supernova explosions associated with star formation. Scientists speculate these factors may play a role in creating the evolutionary trend they observe.

Now that astronomers see this pattern, they can adjust computer simulations of galaxy evolution until these models are able to replicate the observed trend. This will guide scientists to the physical processes most responsible for it.

The DEEP2 survey is led by Lick Observatory at the University of California at Santa Cruz in collaboration with the University of California at Berkeley, the University of Hawaii at Manoa, Johns Hopkins University in Baltimore, Md., the University of Chicago and the California Institute of Technology in Pasadena.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy, Inc. in Washington.




All of this week's top headlines to your email every Friday.


 
 

 

Headlines January 30, 2015

News: Taliban claims responsibility for attack on Americans at military base near airport - The Taliban claimed responsibility Jan. 30 for a shooting incident at a military base attached to Kabul’s international airport yesterday that killed three American civilian contractors and an Afghan national, saying the attacker had infiltrated the ranks of the security forces. Commission...
 
 

News Briefs January 30, 2015

Military judge weighs restrictions on Gitmo female guards A military judge is deciding whether to continue restricting the use of female guards at Guantanamo. Navy Capt. J. Kirk Waits heard closing arguments Jan. 29 at the base in Cuba during a pretrial hearing for Abd al-Hadi al-Iraqi. Waits didn’t say when he will rule. Hadi...
 
 
Air Force photograph by 1st Lt. Jake Bailey

Cope South experts exchange knowledge, techniques

Air Force photograph by 1st Lt. Jake Bailey TSgt. Sam Bishop, center left, and SSgt. Jeffrey Stephens discuss propeller maintenance with Bangladesh air force maintainers, from the 101st Special Flying Unit, during exercise Cope...
 

 

Air Force names 2-star to lead F-35 Integration Office

With the initial operating capability date of the F-35 Lightning II quickly approaching, the Air Force appointed Maj. Gen. Jeffrey Harrigian as the director of a larger Air Force F-35 Integration Office, Feb. 1. In addition to gaining new leadership, the F-35 Integration Office will also grow from a staff of four to 12 and...
 
 
boeing-ana2

Boeing announces ANA’s commitment to more jetliners

Airline continues fleet modernization with Boeing airplanes Boeing and All Nippon Airways announced Jan. 30 the airline’s intent to purchase three 787-10 Dreamliners to add additional flexibility to the airline’s 787 fleet....
 
 
Air Force photograph by Scott M. Ash

Air Force risks becoming too small to succeed under sequestration

Air Force photograph by Scott M. Ash Air Force Chief of Staff Gen. Mark A. Welsh III testifies before the Senate Armed Services Committee Jan. 28, 2015, in Washington, D.C., as Commandant of the Marine Corps Gen. Joesph F. Dunf...
 




0 Comments


Be the first to comment!


Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>