3D shape of Orion A from Gaia DR2^⋆

¹ Universität Wien, Institut für Astrophysik, Türkenschanzstrasse 17, 1180 Wien, Austria
e-mail: josefa.elisabeth.grossschedl@univie.ac.at
² University of Vienna, Research Platform, Data Science @ Uni Vienna, Austria
³ Universidade do Porto, Departamento de Engenharia Física da Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
⁴ Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, Allée Geoffroy Saint-Hilaire, CS 50023, 33615 Pessac Cedex, France
⁵ Universitäts-Sternwarte Ludwig-Maximilians-Universität (USM), Scheinerstr. 1, 81679 München, Germany
⁶ Max-Planck-Fellow, Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany
⁷ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138, USA
⁹ Leiden Observatory, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
¹⁰ University of Milan, Department of Physics, via Celoria 16, 20133 Milan, Italy
¹¹ CENTRA, Universidade de Lisboa, FCUL, Campo Grande, Edif. C8, 1749-016 Lisboa, Portugal
¹² Cavendish Laboratory, University of Cambridge, 19 J.J. Thomson Avenue, Cambridge, CB3 0HE, UK

Received: 18 July 2018
Accepted: 11 August 2018

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.