Evidence Of Gas Flow As Galactic Fuel Found
January 12, 2013

Researchers Find Fresh Gas Supply Surrounding Modern Galaxies

redOrbit Staff & Wire Reports — Your Universe Online

Thanks to observations obtained using the Hubble Space Telescope, researchers have discovered direct, empirical evidence of the existence of gas flows that are consumed by galaxies as fuel.

A team led by Nicolas Lehner, research associate professor at the University of Notre Dame, studied data collected by the telescope´s two ultraviolet spectrographs, the Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph, and discovered “large quantities of cool gas with very low quantities of heavy elements in the gaseous cocoons surrounding modern galaxies,” the South Bend, Indiana school said in a statement Friday.

Since there are no heavy elements present in the gas, it shows the circumgalactic medium of these galaxies had not been strongly processed through stars, Lehner and his colleagues said. Their findings have been submitted to the Astrophysical Journal, and were also presented this week during the 221st meeting of the American Astronomical Society in Long Beach, California.

Additionally, images detailing their findings have been published online.

They were able to identify these gaseous streams near galaxies because of the absorption they imprint on the spectra of distant and bright background quasars. The atoms in the gas subtract amounts of light, and as light from the quasars pass through those gases, “the chemical elements leave characteristic spectral ℠fingerprints´ that allow astronomers to study the physical and chemical properties of the gas,” Marissa Gebhard of Notre Dame News said.

“Lehner and collaborators searched for the signature of gas within about 100,000-300,000 light-years of galaxies, identifying this gas due to its strong hydrogen absorption, a known signature of circumgalactic gas,” she added. “They subsequently determined the amount of "metals" — all elements heavier than hydrogen and helium — in this gas to test whether the circumgalactic matter was being newly accreted from intergalactic space and lacking in metals or being ejected from the galaxies themselves and strong in metals.”

The Notre Dame professor explained astronomers had been searching for these gases for a long time, but were hampered by observational limitations that forced them to seek out the tiny amount of metal they contained — no easy feat, given just how little can actually be discovered in the gases. Now, however, they are able to use the process of ultraviolet spectroscopy to look for the hydrogen absorption in the gases — a method that is not dependent upon the concentration of the metallic elements as an identifying factor.

“Lehner and colleagues estimated the amount of metals in the circumgalactic medium of galaxies over the last six billion years. They found that the distribution of heavy elements abundances in circumgalactic gas has two different characteristic values, around 2 percent and 40 percent of the heavy element content of the sun,” the university said. “Both branches of the metal abundance distribution have a nearly equal number of gas clouds.

“Meanwhile, the circumgalactic gas probed in this study was also found to have a mass comparable to that of all the gas within the galaxies themselves, thus providing a substantial reservoir for fueling continued star formation in modern galaxies,” they added. “This study confirms the earlier finding by the same team that metal-enriched gas is widespread even far from the galaxies themselves, likely sent there by strong outflows driven by supernovae.”