SCUBA observations of the Horsehead Nebula - what did the horse swallow?

Abstract

We present observations taken with SCUBA on the JCMT of the Horsehead Nebula in Orion (B33), at wavelengths of 450 and 850 \mum. We see bright emission from that part of the cloud associated with the photon-dominated region (PDR) at the `top' of the horse's head, which we label B33-SMM1. We characterise the physical parameters of the extended dust responsible for this emission, and find that B33-SMM1 contains a more dense core than was previously suspected. We compare the SCUBA data with data from the Infrared Space Observatory (ISO) and find that the emission at 6.75-\mum is offset towards the west, indicating that the mid-infrared emission is tracing the PDR while the submillimetre emission comes from the molecular cloud core behind the PDR. We calculate the virial balance of this core and find that it is not gravitationally bound but is being confined by the external pressure from the HII region IC434, and that it will either be destroyed by the ionising radiation, or else may undergo triggered star formation. Furthermore we find evidence for a lozenge-shaped clump in the `throat' of the horse, which is not seen in emission at shorter wavelengths. We label this source B33-SMM2 and find that it is brighter at submillimetre wavelengths than B33-SMM1. SMM2 is seen in absorption in the 6.75-\mum ISO data, from which we obtain an independent estimate of the column density in excellent agreement with that calculated from the submillimetre emission. We calculate the stability of this core against collapse and find that it is in approximate gravitational virial equilibrium. This is consistent with it being a pre-existing core in B33, possibly pre-stellar in nature, but that it may also eventually undergo collapse under the effects of the HII region.

arXiv comment11 pages, 6 figures, accepted by MNRAS

References in corpus (10)

• SCUBA: A common-user submillimetre camera operating on the James Clerk Maxwell Telescope
• Are PAHs precursors of small hydrocarbons in Photo--Dissociation Regions? The Horsehead case
• The initial conditions of isolated star formation - VI. SCUBA mapping of prestellar cores
• Inverse temperature dependence of the dust submillimeter spectral index
• The initial conditions of isolated star formation. V: ISOPHOT imaging and the temperature and energy balance of pre-stellar cores
• Carbon budget and carbon chemistry in Photon Dominated Regions
• Density structure of the Horsehead nebula photo-dissociation region
• Large Area Mapping at 850 Microns. IV. Analysis of the Clump Distribution in the Orion B South Molecular Cloud
• Hydrodynamics of photoionized columns in the Eagle Nebula, M 16
• Velocity field and star formation in the Horsehead nebula

Cited by in corpus (27)

• A SCUBA survey of Orion, the low-mass end of the core mass function
• The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects
• Driving Turbulence and Triggering Star Formation by Ionizing Radiation
• Dynamics of Dense Cores in the Perseus Molecular Cloud
• The JCMT Gould Belt Survey: First results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population
• The Virial Balance of Clumps and Cores in Molecular Clouds
• Turbulence and star formation efficiency in molecular clouds: solenoidal versus compressive motions in Orion B
• SCUBA and Spitzer observations of the Taurus molecular cloud - pulling the bull's tail
• The ionization fraction gradient across the Horsehead edge: An archetype for molecular clouds
• The Spitzer survey of interstellar clouds in the Gould Belt. II. The Cepheus Flare observed with IRAC and MIPS
• Excitation of H${}_2$ in photodissociation regions as seen by Spitzer
• Droplets I: Pressure-Dominated Sub-0.1 pc Coherent Structures in L1688 and B18
• Observing a column-dependent zeta in dense interstellar sources: the case of the Horsehead Nebula
• Orbital and physical properties of the $\sigma$ Ori Aa,Ab,B triple system
• Dust processing in photodissociation regions - Mid-IR emission modelling
• Galaxy simulation with the evolution of grain size distribution
• Dissecting the molecular structure of the Orion B cloud: Insight from Principal Component Analysis
• Deuterium fractionation in the Horsehead edge
• Turbulence, Coherence and Collapse: Three Phases for Core Evolution
• Clustering the Orion B giant molecular cloud based on its molecular emission
• An Infrared Census of Star Formation in the Horsehead Nebula
• APEX CO observations towards the photodissociation region of RCW120
• Gas kinematics around filamentary structures in the Orion B cloud
• Magnetic fields in the Horsehead Nebula
• Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula
• What did the seahorse swallow? APEX 170 GHz observations of the chemical conditions in the Seahorse infrared dark cloud
• Triggered Star Formation in the Environment of Young Massive Stars