June 1, 2022 (Nanowerk News) A comprehensive understanding of the evolution of galaxies depends in part on an accurate measurement of the abundance of metals in the intergalactic medium, the space between stars, but dust can prevent observations at optical wavelengths. An international team of astronomers from the University of California, Irvine, Oxford University in England and other institutions discovered evidence of heavier elements in local galaxies, which were found to be deficient in previous studies, by analyzing of infrared data collected during a multi-year campaign. For a recent article in Nature Astronomy (“Gaseous metallicity in ultra-bright infrared galaxies is the result of darkening of dust”), researchers examined five galaxies that are faint at wavelengths. visible but billions of times brighter than the sun in the infrared. Interactions between these galaxies and neighboring star systems cause the gas to move and collapse, creating the conditions for prodigious star formation. NASA’s SOFIA Airborne Observatory allowed an UCI-led team of astronomers to study infrared emissions from five nearby galaxies. The researchers found more metal than expected in the intergalactic medium, a result that would have been difficult to achieve without the power to see infrared radiation through thick galactic dust. (Image: Jim Ross, NASA) “By studying the gas content of these galaxies with optical instruments, astronomers were convinced that they were significantly poor in metals compared to other galaxies of similar mass,” said lead author Nima Chartab. , postdoctoral fellow of the ICU. physics and astronomy. “But when we looked at the emission lines of these dusty galaxies at infrared wavelengths, they allowed us a clear view of them and found no significant metal deficiencies.” To determine the abundance of gaseous metals in the intergalactic medium, astronomers tried to acquire data on the proportions of proxies, oxygen, and nitrogen, because the infrared emissions of these elements are less obscured by galactic dust. “We are looking for evidence of the baryon cycle in which stars process elements such as hydrogen and helium to produce carbon, nitrogen and oxygen,” said co-author Asantha Cooray, a professor of physics and astronomy at the UCI. “Stars eventually become supernovae and explode, and then all this gas on the outskirts of stars becomes clouds that are thrown around. The material they contain is loose and diffuse, but eventually through gravitational perturbations caused by others. as stars move, the gas will begin to clump together and collapse, leading to the formation of new stars. ” Observing this process at infrared wavelengths is a challenge for astronomers because the water vapor in the Earth’s atmosphere blocks radiation in this part of the electromagnetic spectrum, making measurements even of terrestrial telescopes more altitude, such as those at the Keck Observatory in Hawaii, are insufficient. Part of the data set used by the team comes from the now-retired Herschel Space Telescope, but Herschel was not equipped with a spectrometer capable of reading a specific emission line that the ICU-led team needed for its study. The researchers’ solution was to ascend to the sky, reaching more than 45,000 feet above sea level, at the Stratospheric Observatory of Infrared Astronomy, NASA’s Boeing 747 equipped with a 2.5-meter telescope. “It took us almost three years to collect all the data using NASA’s SOFIA observatory, because these flights don’t last all night; they are more in the range of 45 minutes of observation time, so the study needed a lot of flight planning and coordination, “Cooray said. By analyzing infrared emissions, researchers were able to compare the metallicity of its target ultra-bright infrared galaxies with less dusty galaxies with similar mass and star formation rates Chartab explained that these new data show that ultra-bright infrared galaxies are in line with the fundamental relationship of metallicity. determined by star mass, metal abundance, and star formation rate, and new data show that the subabundance of metals derived from optical emission lines is probably due to “a strong “This study is an example in which it was critical for us to use this infrared wavelength to gain a full understanding of what it’s happening in some of these galaxies, “Cooray said. “When optical observations initially came out suggesting that these galaxies had low metals, theorists went and wrote articles, there were a lot of simulations trying to explain what was going on. People thought, ‘Maybe they’re really low-metal galaxies. “But we found that was not the case. Having a complete view of the universe across the entire electromagnetic spectrum is really crucial, I think.