Sunday, September 25, 2016

Star Dates

Massive galaxies may have formed when universe was young

Some of the universe’s most massive galaxies may have formed billions of years earlier than current scientific models predict, according to new research led by a Tufts astrophysicist.

The researchers found a relatively large number of very massive, highly luminous galaxies that existed almost 12 billion years ago. That was when the universe was still very young—about 1.5 billion years old.

“These results appear to disagree with the latest predictions from models of galaxy formation and evolution,” says Danilo Marchesini, an assistant professor of physics and astronomy in the School of Arts and Sciences and lead author on the paper, which was published in the Astrophysical Journal on Dec. 10. “Current understanding of the physical processes responsible in forming such massive galaxies has difficulty reproducing these observations.”

The newly identified galaxies were five to 10 times more massive than our own Milky Way.

By complementing existing data with deep images obtained through a new system of five customized near-infrared filters, the researchers were able to get a more complete view of the galaxy population at this early stage and more accurately characterize the sampled galaxies.

The researchers made another surprising discovery. More than 80 percent of these massive galaxies show very high infrared luminosities, which indicate that the galaxies are extremely active and most likely in a phase of intense growth. Massive galaxies in the local universe are instead quiescent and do not form stars at all.

The researchers cautioned that the distances were determined using spectral energy distribution modeling and have not yet been confirmed using a more accurate spectroscopic method. Such “systemic uncertainties” in the determination of the distances of these galaxies might still allow for approximate agreement between observations and model predictions.

However, the discovery of the existence of such massive, old and very dusty galaxies would itself be a notable discovery. Such a galaxy population has never before been observed.

“Either way, it is clear that our understanding of how massive galaxies form is still far from satisfactory,” says Marchesini.

“The existence of these galaxies so early in the history of the universe, as well as their properties, can provide very important clues on how galaxies formed and evolved shortly after the Big Bang,” he adds.

Collaborating with Marchesini were researchers from Yale University, Carnegie Observatories, Leiden University, Princeton University, the University of Kansas and the University of California-Santa Cruz.

Posted December 14, 2010