Found evidence of the existence of galactic metal, shrouded in dust

(ORDO NEWS) — A deep 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 obstruct 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 that was established in previous studies by analyzing infrared data collected during a multi-year campaign.

The researchers studied five galaxies that are dimmer in visible wavelengths but trillions of times brighter than the Sun in infrared.

The interaction between these galaxies and neighboring star systems leads to the displacement and collapse of gas, creating the conditions for powerful star formation.

To determine the abundance of gas-phase metals in the intergalactic medium, astronomers sought to obtain data on the ratios of oxygen and nitrogen, since the infrared emissions of these elements are less obscured by galactic dust.

Observing this process in infrared wavelengths is challenging for astronomers because the water vapor in the Earth’s atmosphere blocks radiation in this part of the electromagnetic spectrum, making measurements from even the highest ground-based equipment, such as the telescope at the Keck Observatory in Hawaii, inadequate.

Some of the data used by the team came from the now decommissioned Herschel Space Telescope, but it was not equipped with a spectrometer capable of reading the specific line of emission that the team needed for the study.

The astronomers decided to take to the skies over 13 kilometers above sea level on a Stratospheric Observatory for Infrared Astronomy, a NASA Boeing 747 aircraft equipped with a 2.5-meter telescope.

By analyzing infrared emissions, the researchers were able to compare the metallicity of their target superluminous infrared galaxies with less dusty galaxies of similar mass and star formation rate.

These new data show that ultraluminous infrared galaxies conform to a fundamental metallicity ratio determined by stellar mass, metal abundance, and star formation rate.

The new data also show that the lack of metals obtained from optical emission lines is likely caused by “strong dust obscuration associated with stellar flares,” the scientists explain.


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