Far-IR detection of neutral atomic oxygen toward the Horsehead Nebula

We present the first detection of neutral atomic oxygen (P1P2 fine structure line at∼63μm) toward the Horsehead photodissociation region (PDR). The cloud has been mapped with the Spitzer Space Telescope at far-IR (FIR) wavelengths using MIPS in the Spectral Energy Distribution (SED) mode. The [O i]63μm line peaks at the illuminated edge of the cloud at AV≃0.1-0.5 (inwards the gas becomes too cold and outwards the gas density drops). The luminosity carried by the [O i]63μm line represents a significant fraction of the total FIR dust luminosity (I63/IFIR≃4×10 ). We analyze the dust continuum emission and the This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.