Astrophys. J., 812, 75 (2015/October-2)
Velocity-resolved [CII] emission and [CII]/FIR mapping along Orion with Herschel.
GOICOECHEA J.R., TEYSSIER D., ETXALUZE M., GOLDSMITH P.F., OSSENKOPF V., GERIN M., BERGIN E.A., BLACK J.H., CERNICHARO J., CUADRADO S., ENCRENAZ P., FALGARONE E., FUENTE A., HACAR A., LIS D.C., MARCELINO N., MELNICK G.J., MULLER H.S.P., PERSSON C., PETY J., ROLLIG M., SCHILKE P., SIMON R., SNELL R.L. and STUTZKI J.
Abstract (from CDS):
We present the first ∼7.'5x11.'5 velocity-resolved (∼0.2 km/s) map of the [C ii] 158 µm line toward the Orion molecular cloud 1 (OMC 1) taken with the Herschel/HIFI instrument. In combination with far-IR (FIR) photometric images and velocity-resolved maps of the H41α hydrogen recombination and CO J = 2-1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/photodissociation region (PDR)/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the [C ii] luminosity (∼85%) is from the extended, FUV-illuminated face of the cloud (G0> 500, 5x103/cm3) and from dense PDRs ( 104, 105/cm3) at the interface between OMC 1 and the H ii region surrounding the Trapezium cluster. Around ∼15% of the [C ii] emission arises from a different gas component without a CO counterpart. The [C ii] excitation, PDR gas turbulence, line opacity (from [13C ii]), and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the L[C ii]/ and/ ratios and show that L[C ii]/ decreases from the extended cloud component (∼10–2-10–3) to the more opaque star-forming cores (∼1010–4). The lowest values are reminiscent of the ''[C ii] deficit'' seen in local ultraluminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing L[C ii]/ ratio correlates better with the column density of dust through the molecular cloud than with/. We conclude that the [C ii]-emitting column relative to the total dust column along each line of sight is responsible for the observed L[C ii]/ variations through the cloud.
galaxies: ISM - H ii regions - infrared: galaxies - ISM: clouds
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