Journal article, 2015

We present the first ~7.′5 × 11.′5 velocity-resolved (~0.2 km/s) map of the [C II] 158 μm line toward the Orion molecular cloud1 (OMC1) 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, nH > 5 × 10^3 cm^−3) and from dense PDRs (G0>~10^4, nH>~10^5 cm^−3) 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[CII]/LFIR and LFIR/MGas ratios and show that L[CII]/LFIR 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 “[C II] deficit” seen in local ultraluminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing L[C II]/LFIR ratio correlates better with the column density of dust through the molecular cloud than with LFIR/MGas. 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]/LFIR variations through the cloud.

galaxies: ISM – H II regions – infrared: galaxies – ISM: clouds


J.R. Goicoechea

D. Teyssier

M. Etxaluze

P.F. Goldsmith

V. Ossenkopf

M. Gerin

E.A. Bergin

John H Black

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

J. Cernicharo

S. Cuadrado

P. Encrenaz

E. Falgarone

A. Fuente

A. Hacar

D. Lis

N. Marcelino

G.J. Melnick

H.S.P. Müller

Carina Persson

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

J. Pety

M. Röllig

P. Schilke

R. Simon

R.L. Snell

J. Stutzki

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 812 1 75- 75

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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