3D shape of Orion A from Gaia DR2

Josefa E. Grossschedl, Joao Alves, Stefan Meingast, Christine Ackerl, Joana Ascenso, Herve Bouy, Andreas Burkert, Jan Forbrich, Verena Fuernkranz, Alyssa Goodman, Alvaro Hacar, Gabor Herbst-Kiss, Charles J. Lada, Irati Larreina, Kieran Leschinski, Marco Lombardi, Andre Moitinho, Daniel Mortimer, Eleonora Zari

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We use the Gaia DR2 distances of about 700 mid-infrared selected young stellar objects in the benchmark giant molecular cloud Orion A to infer its 3D shape and orientation. We find that Orion A is not the fairly straight filamentary cloud that we see in (2D) projection, but instead a cometary-like cloud oriented toward the Galactic plane, with two distinct components: a denser and enhanced star-forming (bent) Head, and a lower density and star-formation quieter ~75 pc long Tail. The true extent of Orion A is not the projected ~40 pc but ~90 pc, making it by far the largest molecular cloud in the local neighborhood. Its aspect ratio (~30:1) and high column-density fraction (~45%) make it similar to large-scale Milky Way filaments ("bones"), despite its distance to the galactic mid-plane being an order of magnitude larger than typically found for these structures.
Original languageEnglish
Article numberA106
Number of pages9
JournalAstronomy & Astrophysics
Early online date14 Nov 2018
Publication statusE-pub ahead of print - 14 Nov 2018


  • Local insterstellar matter
  • Methods: Observational
  • Methods: Statistical
  • Parallaxes
  • Stars: Distances
  • Stars: Formation


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