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arXiv · 1808.05952

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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Abstract

We use the $\mathit{Gaia}$ 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 $\sim$75 pc long Tail. The true extent of Orion A is not the projected $\sim$40 pc but $\sim$90 pc, making it by far the largest molecular cloud in the local neighborhood. Its aspect ratio ($\sim$30:1) and high column-density fraction ($\sim45\%$) 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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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. 2018-08-17. 3D shape of Orion A from Gaia DR2. https://doi.org/10.1051/0004-6361/201833901

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