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 today at the meeting of the American Astronomical Society in Long Beach, Calif.
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.
"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." The new work uses ultraviolet spectroscopy to identify the gas through its hydrogen absorption, which is independent of the metal content. This has allowed the team for the first time to determine how heavy elements are distributed around galaxies in an unbiased manner.
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. 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. 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. The metal-rich gas likely traces winds and recycled gas from outflows and galaxy interactions. The metal-poor gas is in quantities of metals too low to trace even in very low-metallicity galaxies that are six billion years old or older. It very likely traces cold streams onto galaxies; its properties are in very good agreement with those seen in the computer simulations of galaxy formation and evolution.
"One of the big questions remaining from our study is what types of galaxies are associated with these gas clouds," remarks Lehner. The luminous components of most of the galaxies in the current study have not yet been identified. This team will use the Large Binocular Telescope, Keck and other ground-based telescopes to reveal the nature of the galaxies.
"Independent of the interpretation, our findings place new constraints on our understanding of how elements are distributed around galaxies," Lehner concludes. "There is not only a large mass of metal-rich gas around galaxies in the modern-day universe, but also a significant mass of metal-poor gas that may become available for star formation." This new work also implies the more diffuse intergalactic medium far from galaxies in the modern universe may be far more metal deficient than previously thought.
This research has been funded by NASA and the National Science Foundation, and has made use of the Hubble, Keck and Magellan telescopes. Co-authors include J. Christopher Howk from Notre Dame; Todd Tripp from the University of Massachusetts; Jason Tumlinson from the Space Telescope Science Institute (STScI); J. Xavier Prochaska from the University of California, Santa Cruz; John O'Meara from St. Michael's College; Chris Thom from STScI; Jess Werk from the University of California, Santa Cruz; Andrew Fox from STScI; and Joe Ribaudo from Utica College.
Nicholas Lehner | EurekAlert!
A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne
Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology