Using NASA’s SOFIA observatory and other data resources, an international team of astronomers discovered evidence of metals in local galaxies, which had previously been overlooked in previous studies, by examining infrared data collected over a multiyear campaign.
A precise assessment of the quantity of metals in the intergalactic medium (the space between stars) is required for a full knowledge of galaxy history, yet dust can obstruct optical wavelength observations. By analyzing infrared data collected over a multiyear campaign, 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 had previously been found to be lacking in previous studies.
The researchers analyzed five galaxies that are dull in optical wavelengths but trillions of times more bright than the sun in the infrared for a report published recently in Nature Astronomy. Interactions between these galaxies and surrounding star systems cause gas to move and collapse, allowing for massive star formation.
“When astronomers examined the gas content of these galaxies with optical tools, they were sure that they were notably metal-poor when compared to other galaxies of similar mass,” said lead author Nima Chartab, a UCI postdoctoral scholar in physics and astronomy. “However, when we analyzed emission lines of these dusty galaxies in infrared wavelengths, we were able to see them well and discovered no major metal deficiency.”
We’re seeking for evidence of baryon cycling, which occurs when stars metabolize elements like hydrogen and helium to make carbon, nitrogen, and oxygen. The stars finally explode as supernovae, and all of the gas on the edges of the stars is converted into clouds that are hurled around.
Professor Asantha Cooray
To determine the abundance of gas-phase metals in the intergalactic medium, the astronomers sought to acquire data on the ratios of proxies, oxygen and nitrogen, because infrared emissions from these elements are less obscured by galactic dust.
“We’re seeking for evidence of baryon cycling, which occurs when stars metabolize elements like hydrogen and helium to make carbon, nitrogen, and oxygen,” said co-author and UCI professor of physics and astronomy Asantha Cooray. “The stars finally explode as supernovae, and all of the gas on the edges of the stars is converted into clouds that are hurled around. The material within them is loose and diffuse, but because to gravitational disturbances generated by the movement of other stars, the gas will eventually clump and collapse, resulting in the birth of new stars.”
Observing this process in infrared wavelengths is difficult for astronomers because water vapor in the Earth’s atmosphere blocks radiation in this part of the electromagnetic spectrum, rendering measurements from even the highest-altitude ground telescopes, such as those at Hawaii’s Keck Observatory, insufficient.
The scientists used data from the now-retired Herschel Space Telescope, but Herschel did not have a spectrometer capable of measuring a specific emission line that the UCI-led team required for its study. The researchers’ idea was to take to the skies in the Stratospheric Observatory for Infrared Astronomy, NASA’s Boeing 747 equipped with a 2.5-meter telescope, reaching more than 45,000 feet above sea level.
“It took us nearly three years to collect all the data in utilizing NASA’s SOFIA observatory,” Cooray explained. “Because these flights don’t stay all night; they’re more in the region of 45 minutes of observing time, so the study required a lot of flight planning and cooperation.”
The researchers were able to compare the metallicity of their target ultraluminous infrared galaxies with less dusty galaxies of similar mass and star formation rates by examining infrared emissions. According to Chartab, the new data demonstrate that ultraluminous infrared galaxies follow the fundamental metallicity relation, which is determined by stellar mass, metal abundance, and star formation rate.
According to the paper, the new data also suggest that the lack of metals obtained from optical emission lines is likely owing to “severe dust obscuration associated with starburst.”
“In this work, it was crucial for us to use this infrared wavelength to have a thorough picture of what’s going on in some of these galaxies,” Cooray explained. “When the optical measurements first suggested that these galaxies had low metals, theorists authored articles and ran simulations to try to understand what was going on. People speculated, ‘Perhaps they really are low-metal galaxies,’ but we discovered that this was not the case. I believe that having a complete picture of the universe over the entire electromagnetic spectrum is critical.”
