The COMplexity of Orion : An ALMA view
Séminaire IPAG de Laurent Pagani (LERMA), jeudi 8 novembre 2018 à 11h00, salle Manuel Forestini
Orion KL is the closest (400 pc) of all the massive star forming regions and allows therefore detailed studies. Despite its closeness, its complexity still calls for interferometric observations in order to separate the different subregions emitting at different velocities, which are otherwise mixed in an inextricable combination of different species at similar apparent frequencies in single dish observations. Orion KL has another peculiarity : it has undergone an explosive event 500 years ago as revealed by H2 and CO maps, and also by the proper motion of three stellar objects, BN, I and n.
While our ALMA observations were mostly aimed at detecting the rare isotopologue 16O18O to follow up on our Herschel detection of O2 towards this region (Goldsmith et al. 2011, Chen et al. 2014), we took the advantage of that deep search to observe 16 GHz of spectral band in the 1.3 mm window. We did not detect 16O18O but the quality of our data (a 5-fold improvement compared to the similar data taken during Science Verification 0) allowed us to identify a few species not detected yet in Orion, and study the kinematics of the region in detail. In particular, we report gGg’ ethylene glycol and acetic acid detections in a peculiar place, and we explain the line position and shape of each subregion, both in relation with the 500 years-old explosion. We show that based on this kinematics, we can make a 3D description of the region.
The data quality is high enough to also study each species channel-wise. This reveals gas expansions never seen before which are traceable back to the explosion center. These expansions are comparable to time-of-flight experiments in the laboratory and allow therefore to establish the order of evolution between species, from those that are destroyed soon after their sublimation from the ices to those which survive until they get too diluted to be observed. This brings interesting clues to the chemistry of hot regions, and in particular of complex organic molecules (COMs). For example, we think that a route exists to produce ethyl cyanide in the gas phase (as also advocated by Suzuki et al. 2018).