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Grossschedl, Josefa E.; Alves, Joao; Meingast, Stefan; Ackerl, Christine; Ascenso, Joana; Bouy, Herve; Burkert, Andreas; Forbrich, Jan; Fürnkranz, Verena; Goodman, Alyssa; Hacar, Alvaro; Herbst-Kiss, Gabor; Lada, Charles J.; Larreina, Irati; Leschinski, Kieran; Lombardi, Marco; Moitinho, Andre; Mortimer, Daniel; Zari, Eleonora (2018): 3D shape of OrionA from Gaia DR2. In: Astronomy & Astrophysics, Vol. 619, A106
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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 similar to 75 pc long Tail. The true extent of Orion A is not the projected similar to 40 pc but similar to 90 pc, making it by far the largest molecular cloud in the local neighborhood. Its aspect ratio (similar to 30: 1) and high column-density fraction (similar to 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.