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arXiv · 1508.03801

Velocity-resolved [CII] emission and [CII]/FIR Mapping along Orion with Herschel

J. R. Goicoechea·D. Teyssier·M. Etxaluze·P. F. Goldsmith·V. Ossenkopf·M. Gerin·E. A. Bergin·J. H. Black·J. Cernicharo·S. Cuadrado·P. Encrenaz·E. Falgarone·A. Fuente·A. Hacar·D. C. Lis·N. Marcelino·G. J. Melnick·H. S. P. Muller·C. Persson·J. Pety·M. Rollig·P. Schilke·R. Simon·R. L. Snell·J. Stutzki
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Abstract

We present the first 7.5'x11.5' velocity-resolved map of the [CII]158um line toward the Orion molecular cloud-1 (OMC-1) taken with the Herschel/HIFI instrument. In combination with far-infrared (FIR) photometric images and velocity-resolved maps of the H41alpha hydrogen recombination and CO J=2-1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/PDR/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the [CII] luminosity (~85%) is from the extended, FUV-illuminated face of the cloud G_0>500, n_H>5x10^3 cm^-3) and from dense PDRs (G_0~10^4, n_H~10^5 cm^-3) at the interface between OMC-1 and the HII region surrounding the Trapezium cluster. Around 15% of the [CII] emission arises from a different gas component without CO counterpart. The [CII] excitation, PDR gas turbulence, line opacity (from [13CII]) and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the [CII]/FIR and FIR/M_Gas ratios and show that [CII]/FIR decreases from the extended cloud component (10^-2-10^-3) to the more opaque star-forming cores (10^-3-10^-4). The lowest values are reminiscent of the "[CII] deficit" seen in local ultra-luminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing [CII]/FIR ratio correlates better with the column density of dust through the molecular cloud than with FIR/M_Gas. We conclude that the [CII] emitting column relative to the total dust column along each line of sight is responsible for the observed [CII]/FIR variations through the cloud.

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J. R. Goicoechea, D. Teyssier, M. Etxaluze, P. F. Goldsmith, V. Ossenkopf, M. Gerin, E. A. Bergin, J. H. Black, J. Cernicharo, S. Cuadrado, P. Encrenaz, E. Falgarone, A. Fuente, A. Hacar, D. C. Lis, N. Marcelino, G. J. Melnick, H. S. P. Muller, C. Persson, J. Pety, M. Rollig, P. Schilke, R. Simon, R. L. Snell, J. Stutzki. 2015-08-16. Velocity-resolved [CII] emission and [CII]/FIR Mapping along Orion with Herschel. https://doi.org/10.1088/0004-637x%2F812%2F1%2F75

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