Around modern galaxies, a lot of gas

Led by Nicolas Lehner, research associate and professor, University of Notre Dame, the team's observations using Hubble's ultraviolet Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph, show large quantities of cool gas with very low quantities of heavy elements in the gaseous cocoons surrounding modern galaxies.

The lack of heavy elements indicates this gas has not been strongly processed through stars. Astronomers identified gaseous streams near galaxies through the absorption they imprint on the spectra of distant, bright background quasars, the Astrophysical Journal reports.

The atoms in the gas remove small amounts of the light, and as the light from the quasars passes through the gas around galaxies, the chemical elements leave characteristic spectral "fingerprints" that allow astronomers to study the physical and chemical properties of the gas, according to a Notre Dame statement.

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.

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.

"Astronomers have been searching for this infalling gas for a while," notes Lehner. "However, due to observational limitations, they had to search for metal-poor gas using the metals themselves. Since there is a tiny amount of metals in this gas, it was difficult to find in that way."

These findings were presented at the recent meeting of the American Astronomical Society in Long Beach, California.