Astronomers find surprising trend in galaxy evolution

A COMPREHENSIVE study of hundreds of galaxies observed by the Keck telescopes in Hawaii and the United States National Aeronautics and Space Administration (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 Centre in Greenbelt, and the study’s lead researcher in a statement made available to The Guardian over the weekend by the agency.

She added: “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 colour 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 organisation.

Meanwhile, NASA is accepting applications from graduate and undergraduate university students to fly experiments to the edge of space on a scientific balloon next year. The balloon competition is a joint project between NASA and the Louisiana Space Consortium (LaSPACE) in Baton Rouge.

The space agency is targeting fall 2013 for the next flight opportunity for the High Altitude Student Platform (HASP). HASP is a balloon-borne instrument stack that provides an annual near-space flight opportunity for 12 instruments built by students.

It said A panel of experts from NASA’s Wallops Flight Facility in Virginia and LaSPACE would review the applications and select the finalists for the next flight opportunity.

Flights are launched from the Columbia Scientific Balloon Facility’s remote site in Fort Sumner, N.M., and typically achieve 15 to 20 hours’ duration at an altitude of about 23 miles.

HASP houses and provides power, mechanical support, interactivity and communications for the instruments. It can be used to flight-test compact satellites, prototypes and other small payloads designed and built by students.

HASP can support about 200 pounds for payloads and test articles. Since 2006, the HASP program has flown 60 payloads involving more than 500 students from 14 states, Puerto Rico and Canada.

The deadline for applications for the 2013 flight is Dec. 14. A question-and-answer teleconference for interested parties will be held November 16.

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 two billion and 8 billion light-years away, the galaxies have stellar masses ranging from about 0.3 percent to 100 per cent of the mass of our home galaxy.

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 (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy, Inc. in Washington.


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