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Astronomy team discovers evidence of galactic metal shrouded in dust

Astronomy team discovers evidence of galactic metal shrouded in dust
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NASA’s SOFIA airborne observatory enabled a 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 ability to view infrared radiation through thick galactic dust. Credit: Jim Ross/NASA

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, researchers examined five dark galaxies in visible wavelengths but trillions of times brighter than the sun in the infrared. The interactions between these galaxies and their neighbors star systems cause the gas to move and collapse, creating the conditions for prodigious star formation.

“Studying the gas content of these galaxies with optical instrumentsastronomers were convinced they were significantly metal-poor compared to other galaxies of similar mass,” said lead author Nima Chartab, UCI postdoctoral researcher in physics and astronomy. “But when we observed the d emission from these dusty galaxies in infrared wavelengthswe had a clear view of them and found no significant metal deficiencies.”

To determine the abundance of metals in the gas phase in the intergalactic mediumastronomers have sought to acquire data on the ratios of proxies, oxygen and nitrogen, because 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,” said co-author Asantha Cooray, professor of physics and astronomy at the UCI. “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 by gravitational disturbances caused by other stars moving in, 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 vapour in the Earth’s atmosphere blocks radiation on this part of the electromagnetic spectrum, making measurements by ground-based telescopes even at the highest 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 – more than 45,000 feet above sea level – in the Stratospheric Infrared Astronomy Observatory, NASA’s Boeing 747 telescope-equipped 2. 5 meters.

“It took us almost three years to collect all the data using NASA’s SOFIA Observatory because these flights are not all night; they are more like 45 minutes of observing time, so the study took a lot of planning and coordination flight,” 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 show that the underabundance of metals derived from optical emission lines is likely due to “heavy 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 that 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. galaxies‘, but we found that this was not the case. Having a complete view of the universe across the entire electromagnetic spectrum is really crucial, I think.”


The far-infrared emission from galaxies with active supermassive black holes


More information:
Nima Chartab et al, Low gas-phase metallicities of ultrabright infrared galaxies are the result of dust obscuration, natural astronomy (2022). DOI: 10.1038/s41550-022-01679-y

Quote: Astronomy team finds evidence of dust-shrouded galactic metal (June 1, 2022) Retrieved June 2, 2022 from https://phys.org/news/2022-06-astronomy-team-evidence-galactic-metal .html

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