Massive Supply of Gas Around Modern Galaxies |
Galaxies have a voracious appetite for fuel — in this case, fresh gas — but astronomers have had difficulty finding the pristine gas that should be falling onto galaxies. Now, scientists have provided direct empirical evidence for these gas flows using new observations from the Hubble Space Telescope.
The team led by Nicolas Lehner, research associate professor at the University of Notre Dame, is presenting its work January 11 at the meeting of the American Astronomical Society in Long Beach, Calif.
The team’s observations using Hubble’s two ultraviolet spectrographs, the 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 in the circumgalactic medium of the galaxies has not been strongly processed through stars. The members’ work, “The Bimodal Metallicity Distribution of the Cool Circumgalactic Medium at z<1,” has been submitted to the Astrophysical Journal.
Led by Lehner, the team of astronomers identified gaseous streams near galaxies through the absorption they imprint on the spectra of distant, bright background quasars. 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. 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. continue reading