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| EPoS Contribution |
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Outstanding Radio-Imaging of OrioN-B: Characterizing the Different Environments of a GMC
Jan Orkisz IRAM, Grenoble, FR | |
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Giant molecular clouds (GMC) are known to exhibit a complex structure,
shaped by turbulence, gravity and magnetic fields. From the most diffuse
enveloppe to the densest cores, GMCs harbour large gas density
variations, but also strong temperature gradients and dramatically
different chemical environments. To better understand the transition
from one environment to another, and eventually the path that leads to
star formation, the different environments present in a GMC must be
precisely identified and characterized.
The ORION-B project (Outstanding Radio-Imaging of OrioN B) currently uses the IRAM-30m/EMIR 3mm receiver to image a field of 5 square degrees, located near the southern edge of the Orion B molecular cloud, including the Horsehead nebula, NGC 2023, and NGC 2024. The total frequency bandwidth of 32 GHz has been observed with a spectral resolution of 195 kHz (0.6 km/s), a typical spatial resolution of 27" (i.e., 50 mpc or 104 AU at 400 pc - the distance of Orion B), and a typical sensitivity of 0.1 K. We succeeded to image the J=1-0 line of the isotopologues of CO as well as the 3mm lines of HCO+, HCN, HNC, CN, CCH, C3H2, CS, SO, N2H+, SiO, CH3OH, and many other weaker features. We aim at adapting to astronomical data statistical methods and machine learning tools to finely characterize the structure, chemistry and dynamics of this particular GMC, and identify new molecular diagnostics that could be used in a wide variety of regions. This detailed bench- marking of available line diagnostics will allow to fully-exploit the possibilities offered by the new generation of (sub-)millimeter receivers in observations of galactic and extra-galactic star forming regions. This talk summarizes the team results. First, we show how tracers of different optical depth like the CO isotopologues allow us to fully trace the molecular medium, from the diffuse envelope to the dense cores, while various chemical tracers can be used to reveal different environments. A clustering algorithm applied to the intesities of selected molecular lines reveals spatially continuous regions characterized e.g. by their mean extinction, density or UV illumination. Conversely, a global Principal Component Analysis of the line integrated brightnesses reveals which are the combinations of lines sensitive to the column density, the density, and the UV field. Making use of the 13CO(1-0) line, we are able to characterize the ratio of compressive vs. solenoidal motions in the turbulent flow, and to relate this to the star formation efficiency in various regions of Orion B. The dynamics of the filamentary network in the Orion B cloud, identified using the C18O(1-0) line, also bear information on the filaments' origin, and show several possible mechanisms of dense core formation in filaments. | |
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| Caption: Many approaches to characterize the ORION-B dataset. Left: the kinematics of the 13CO(1-0) datacube colour-coded for radial velocities comprised between 5.7 (blue) and 13.7 (red) km/s. Middle: Encoding the linear combination of the three main principal components (PCs, which represent column density, volume density and UV illumination) in the colour space, by using the luminosity (PC1) and two axes of hue (PC2 and PC3). Right: Segmenting the field into regions of increasing (column) density by clustering the emission of CO isotopologues. | |
| Collaborators: J. Pety, IRAM, FR M. Gerin, ENS/Obs Paris, FR E. Bron, ICMM, ES S. Bardeau, IRAM, FR J. Goicoechea, ICMM, ES P. Gratier, U Bordeaux, FR V. Guzman, ALMA JAO, CL F. Le Petit, Obs Paris, FR F. Levrier, ENS/Obs Paris, FR H. Liszt, NRAO, US K. Öberg, Harvard, US E. Roueff, Obs Paris, FR N. Peretto, U Cardiff, UK A. Sievers, IRAM, ES P. Tremblin, Maison de la Simulation, FR |
Key publication
Suggested Session: Molecular clouds |