3D shape of Orion A from Gaia DR2
Meingast, Stefan; Alves, João; Bouy, Hervé; Forbrich, Jan; Lada, Charles J.; Lombardi, Marco; Goodman, Alyssa; Zari, Eleonora; Großschedl, Josefa E.; Ackerl, Christine; Ascenso, Joana; Burkert, Andreas; Fürnkranz, Verena; Hacar, Álvaro; Herbst-Kiss, Gabor; Larreina, Irati; Leschinski, Kieran; Moitinho, André; Mortimer, Daniel
Austria, Portugal, France, Germany, United Kingdom, United States, Netherlands, Italy
Abstract
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.
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