Herschel CHESS discovery of the fossil cloud that gave birth to the Trapezium and Orion KL

Abstract

As part of the Herschel Guaranteed Time Key Programme CHESS, we present the discovery of a diffuse gas component in the foreground of the intermediate-mass protostar OMC-2 FIR 4, located in the Orion A region. Making use of the full HIFI spectrum of OMC-2 FIR 4 obtained in CHESS, we detected several ground-state lines from OH+, H2O+, HF, and CH+, all of them seen in absorption against the dust continuum emission of the protostar's envelope. The lines peak at a velocity of 9 km/s, which is blue-shifted by 2 km/s with respect to the systemic velocity of OMC-2 FIR 4 (V = 11.4 km/s). We derived column densities for each species, as well as an upper limit to the column density of the undetected H3O+. In order to model and characterise the foreground cloud, we used the Meudon PDR code to run a homogeneous grid of models that spans a reasonable range of densities, visual extinctions, cosmic ray ionisation rates and far-ultraviolet (FUV) radiation fields. The results of our modelling indicate that the foreground cloud is composed of predominantly neutral diffuse gas (n(H) = 100 cm-3) and is heavily irradiated by an external source of FUV that most likely arises from the nearby Trapezium OB association. The cloud is 6 pc thick and bears many similarities with the so-called C+ interface between Orion-KL and the Trapezium cluster, 2 pc south of OMC-2 FIR 4. We conclude that the foreground cloud we detected is an extension of the C+ interface seen in the direction of Orion KL, and interpret it to be the remains of the parental cloud of OMC-1, which extends from OMC-1 up to OMC-2.

10 pages, 6 figures, accepted by Astronomy and Astrophysics

References in corpus (4)

• The distance to the Orion Nebula
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• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Models of turbulent dissipation regions in the diffuse interstellar medium

Cited by in corpus (15)

• Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
• Fragmentation of massive dense cores down to ~1000 AU: Relation between fragmentation and density structure
• SOLIS II. Carbon-chain growth in the Solar-type protocluster OMC2-FIR4
• Stellar disk destruction by dynamical interactions in the Orion Trapezium star cluster
• SOLIS IV. Hydrocarbons in the OMC-2 FIR 4 region, a probe of energetic particle irradiation of the region
• Carbon isotopic fractionation in molecular clouds
• Spatially extended OH+ emission from the Orion Bar and Ridge
• Organic chemistry in the protosolar analogue HOPS-108: Environment matters
• The Herschel/HIFI spectral survey of OMC-2 FIR 4 (CHESS): An overview of the 480 to 1902 GHz range
• Herschel/HIFI Spectral Mapping of C${}^{+}$, CH${}^{+}$, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH${}^{+}$ Formation
• Herschel Planetary Nebula Survey (HerPlaNS) - First Detection of OH+ in Planetary Nebulae
• Dusty spirals versus gas kinematics in the inner kiloparsec of Four Low-Luminosity Active Galactic Nuclei
• First survey of HCNH${}^{+}$ in high-mass star-forming cloud cores
• OMC-2 FIR 4 under the microscope: Shocks, filaments, and a highly collimated jet at 100 au scales
• Three-dimensional distribution of hydrogen fluoride gas toward NGC6334 I and I(N)