MSGID: 1:317/3 644605e5   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Making better measurements of the composition of galaxies    
      
     Date:   
         April 23, 2023   
     Source:   
         University of California - Davis   
     Summary:   
         A study using data from telescopes on Earth and in the sky resolves   
         a problem plaguing astronomers working in the infrared and could   
         help make better observations of the composition of the universe   
         with the James Webb Space Telescope and other instruments.   
      
      
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   FULL STORY   
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   A study using data from telescopes on Earth and in the sky resolves a   
   problem plaguing astronomers working in the infrared and could help make   
   better observations of the composition of the universe with the James   
   Webb Space Telescope and other instruments. The work is published April   
   20 in Nature Astronomy.   
      
   "We're trying to measure the composition of gases inside galaxies," said   
   Yuguang Chen, a postdoctoral researcher working with Professor Tucker   
   Jones in the Department of Physics and Astronomy at the University of   
   California, Davis.   
      
   Most elements other than hydrogen, helium and lithium are produced   
   inside stars, so the composition and distribution of heavier elements   
   -- especially the ratio of oxygen to hydrogen -- can help astronomers   
   understand how many and what kinds of stars are being formed in a   
   distant object.   
      
   Astronomers use two methods to measure oxygen in a galaxy, but   
   unfortunately, they give different results. One common method,   
   collisionally excited lines, gives a strong signal, but the results   
   are thought to be sensitive to temperature changes, Chen said. A second   
   method uses a different set of lines, called recombination lines, which   
   are fainter but not thought to be affected by temperature.   
      
   The recombination line method consistently produces measurements about   
   double those from collisionally excited lines. Scientists attribute the   
   discrepancy to temperature fluctuations in gas clouds, but this has not   
   been directly proven, Chen said.   
      
   Chen, Jones and colleagues used optical and infrared astronomy to measure   
   oxygen abundance in dwarf galaxy Markarian 71, about 11 million light   
   years from Earth. They used archived data from the recently retired   
   SOFIA flying telescope and the retired Herschel Space Observatory, as   
   well as making observations with telescopes at the W.M. Keck Observatory   
   in Mauna Kea, Hawaii.   
      
   SOFIA (Stratospheric Observatory For Infrared Astronomy) was a telescope   
   mounted in a Boeing 747 aircraft. By flying at 38,000 to 45,000 feet, the   
   aircraft could get above 99% of the water vapor in Earth's atmosphere,   
   which effectively blocks infrared light from deep space from reaching   
   ground level. A joint project of NASA and the German space agency,   
   SOFIA made its last operational flight in September 2022 and is now   
   headed for a museum display in Tucson.   
      
   The Herschel Space Observatory, named after astronomers William and   
   Caroline Herschel, was an infrared space telescope operated by the   
   European Space Agency. It was active from 2009 to 2013.   
      
   A surprising result With data from these instruments, Chen and Jones   
   examined oxygen abundance in Markarian 71 while correcting for temperature   
   fluctuations. They found that the result from collisionally excited   
   infrared lines was still 50% less than that from the recombination line   
   method, even after eliminating the effect of temperature.   
      
   "This result is very surprising to us," Chen said. There is no consensus   
   on an explanation for the discrepancy, he said. The team plans to look   
   at additional objects to figure out what properties of galaxies correlate   
   with this variation, Chen said.   
      
   One of the goals of the James Webb Space Telescope, launched in 2022,   
   is to make infrared observations of the composition of distant galaxies   
   in the first billion years of the universe. The new results provide a   
   framework for making these measurements with the JWST and the Atacama   
   Large Millimeter Array in Chile.   
      
   Additional co-authors on the paper are: Ryan Sanders and Erin Huntzinger,   
   UC Davis; Dario Fadder, Jessica Sutter and Robert Minchin, SOFIA Science   
   Center, NASA Ames Research Center; Peter Senchyna, Observatories of   
   the Carnegie Institute for Science, Pasadena; Daniel Stark and Benjamin   
   Weiner, Steward Observatory, University of Arizona; Justin Spilker, Texas   
   A&M University; and Guido Roberts-Borsani, UCLA. The work was financially   
   supported in part by NASA. SOFIA was jointly operated by the Universities   
   Space Research Association, Inc., and the Deutsches SOFIA Institut.   
      
   The W.M. Keck Observatory is operated as a scientific partnership among   
   the California Institute of Technology, the University of California,   
   and NASA, with financial support from the W.M. Keck Foundation. The   
   researchers would like to thank the Hawaiian community for the privilege   
   of allowing them to conduct observations on Mauna Kea, which plays a   
   significant cultural and religious role.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Space_Telescopes # NASA # Space_Exploration # Astronomy   
                   # Astrophysics # Space_Station # Satellites # Galaxies   
       * RELATED_TERMS   
             o Spitzer_space_telescope o Active_optics o Radio_telescope o   
             Hubble_Deep_Field o Telescope o Astronomy o Space_observatory   
             o Shape_of_the_Universe   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_California_-_Davis. Note: Content may be edited for style   
   and length.   
      
      
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   Journal Reference:   
      1. Yuguang Chen, Tucker Jones, Ryan Sanders, Dario Fadda, Jessica   
      Sutter,   
         Robert Minchin, Erin Huntzinger, Peter Senchyna, Daniel Stark,   
         Justin Spilker, Benjamin Weiner, Guido Roberts-Borsani. Accurate   
         oxygen abundance of interstellar gas in Mrk 71 from   
         optical and infrared spectra. Nature Astronomy, 2023; DOI:   
         10.1038/s41550-023-01953-7   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230423213913.htm   
      
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