UCI-led astronomy team discovers evidence of galactic metal shrouded in dust – EurekAlert


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Infrared Emissions Reveal Unseen Secrets With Optical Wavelength Observations
University of California – Irvine
Irvine, California, June 1, 2022 – A thorough understanding of galaxy evolution depends in part on accurately measuring the abundance of metals in the intergalactic medium – the space between stars – but dust can hamper observations at optical wavelengths. An international team of astronomers from the University of California at Irvine, the University of Oxford in England and other institutions have found evidence of heavier elements in local galaxies – found to be deficient in previous studies – by analyzing the infrared data collected during a multi-year campaign.
For an article recently published in natural astronomy, the researchers examined five galaxies that are faint in the visible wavelengths but billions of times brighter than the sun in the infrared. Interactions between these galaxies and nearby star systems cause the gas to shift and collapse, creating the conditions for prodigious star formation.
“By studying the gas content of these galaxies with optical instruments, astronomers were confident that they were significantly metal-depleted compared to other galaxies of similar mass,” the lead author said. Nima Table, UCI postdoctoral researcher in physics and astronomy. “But when we observed the emission lines from these dusty galaxies in the infrared wavelengths, we got a clear view of them and found no significant metal deficiencies.”
To determine the abundance of gas-phase metals in the intergalactic medium, astronomers have sought to acquire data on the ratios of proxies, oxygen, and nitrogen, since 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 like hydrogen and helium to produce carbon, nitrogen and oxygen,” the co-author said. Asantha Cooray, UCI professor of physics and astronomy. “Stars eventually become supernovae and explode, and then all that gas on the outskirts of stars turns into clouds that are thrown up. The material in them is loose and diffuse, but eventually, because of the disturbances gravity caused by other stars moving, the gas will begin to clump together and collapse, leading to the formation of new stars.
Observing this process in infrared wavelengths is a challenge for astronomers, because water vapor in the Earth’s atmosphere blocks radiation on this part of the electromagnetic spectrum, making measurements from terrestrial telescopes even at the higher altitudes – such as those at the Keck Observatory in Hawaii – insufficient.
Part of the dataset used by the team came from the now-retired Herschel Space Telescope, but Herschel was not equipped with a spectrometer capable of reading a specific emission line which the team led by the UCI needed for its study. The researchers’ solution was to soar – reaching more than 45,000 feet above sea level – into the Stratospheric observatory for infrared astronomyNASA’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 on the order of 45 minutes of observing time, so the study required a lot of flight planning and coordination,” Cooray said.
By analyzing the infrared emissions, the researchers were able to compare the metallicity of their target ultrabright infrared galaxies with less dusty galaxies with similar masses and star formation rates. Chartab explained that these new data show that ultrabright infrared galaxies conform to the fundamental metallicity relationship determined by stellar mass, metal abundance and star formation rate.
The new data further shows that the underabundance of metals derived from optical emission lines is likely due to “dust obscuration associated with starbursts,” according to the paper.
“This study is an example where it was critical for us to use this infrared wavelength to fully understand what’s going on in some of these galaxies,” Cooray said. “When the optical observations first came out suggesting these galaxies had little metal in them, theorists went to write papers, there were a lot of simulations trying to explain what was going on. People thought, “Maybe these really are low-metal galaxies,” but we found that wasn’t the case. Having a complete view of the universe across the entire electromagnetic spectrum is really crucial, I think.
UCI physics and astronomy undergraduate students Jonathan Lopez and Preston Zilliot joined Chartab and Cooray in the study, which was partially funded by NASA; Hooshang Nayyeri, UCI; Jingzhe Ma, Harvard University; Dario Fadda of the SOFIA Science Center; Matthew Malkan, UCLA; Dimitra Rigopoulou, University of Oxford, UK; Kartik Sheth, NASA; Julie Wardlow, Lancaster University, UK; and Rodrigo Herrera-Camus, Concepcion University, Chile.
About University of California, Irvine: Founded in 1965, UCI is the youngest member of the prestigious Association of American Universities and is ranked among the top 10 public universities in the nation by US News and World Report. The campus has produced five Nobel laureates and is known for its academic achievement, leading research, innovation, and anteater mascot. Led by Chancellor Howard Gillman, UCI has more than 36,000 students and offers 224 degree programs. It is located in one of the safest and most vibrant communities in the world and is the second largest employer in Orange County, contributing $7 billion annually to the local economy and $8 billion globally. of State. To learn more about the UCI, visit www.uci.edu.
Media access: Radio programs/stations may, for a fee, use an on-campus ISDN line to interview UCI faculty and experts, subject to availability and university approval. For more UCI news, visit news.uci.edu. Additional resources for journalists can be found at communications.uci.edu/for-journalists.
natural astronomy
10.1038/s41550-022-01679-y
Observational study
The faint gas-phase metallicities of ultraluminous infrared galaxies are the result of dust obscuration
26-May-2022
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Media Contact
Brian Bell
University of California – Irvine
bpbell@uci.edu
Cell: 949-565-5533

University of California – Irvine
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