Physical Conditoins in Orion's Veil II: A Multi-Component Study of the Line of Sight Toward the Trapezium

Abstract

Orion's Veil is an absorbing screen that lies along the line of sight to the Orion H II region. It consists of two or more layers of gas that must lie within a few parsecs of the Trapezium cluster. Our previous work considered the Veil as a whole and found that the magnetic field dominates the energetics of the gas in at least one component. Here we use high-resolution STIS UV spectra that resolve the two velocity components in absorption and determine the conditions in each. We derive a volume hydrogen density, 21 cm spin temperature, turbulent velocity, and kinetic temperature, for each. We combine these estimates with magnetic field measurements to find that magnetic energy significantly dominates turbulent and thermal energies in one component, while the other component is close to equipartition between turbulent and magnetic energies. We observe molecular hydrogen absorption for highly excited v, J levels that are photoexcited by the stellar continuum, and detect blueshifted S III and P III. These ions must arise from ionized gas between the mostly neutral portions of the Veil and the Trapezium and shields the Veil from ionizing radiation. We find that this layer of ionized gas is also responsible for He I absorption in the Veil, which resolves a 40-year-old debate on the origin of He I absorption towards the Trapezium. Finally, we determine that the ionized and mostly atomic layers of the Veil will collide in less than 85,000 years.

arXiv comment43 pages, 15 figures, to be published in ApJ

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• Orion's Bar: Physical Conditions across the Definitive H+ / H0 / H2 Interface
• Effects of Magnetic Field Strength and Orientation on Molecular Cloud Formation
• PDRs4All: A JWST Early Release Science Program on radiative feedback from massive stars
• The three dimensional dynamic structure of the inner Orion Nebula
• Tearing the Veil: interaction of the Orion Nebula with its neutral environment
• Spitzer reveals what's behind Orion's Bar
• Spectrophotometry of the Huygens Region of the Orion Nebula, the Extended Orion Nebula, and M~43; Scattered Light Systematically Distorts Conditions Derived from Emission-Lines
• Rotationally Warm Molecular Hydrogen in the Orion Bar
• Synthetic observations of star formation and the interstellar medium
• Molecular globules in the Veil bubble of Orion. IRAM 30m 12CO, 13CO, and C18O 2-1 expanded maps of Orion A
• Pumping up the [N I] nebular lines
• Herschel/HIFI Spectral Mapping of C${}^{+}$, CH${}^{+}$, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH${}^{+}$ Formation
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• The structure of the Orion Nebula in the direction of Theta 1 Ori C
• The Nature and Frequency of Outflows from Stars in the Central Orion Nebula Cluster
• Carbon radio recombination lines from gigahertz to megahertz frequencies towards Orion A
• Deciphering the 3-D Orion Nebula-I: Expanding Shells in the Huygens Region
• Orion's Veil: Magnetic field strengths and other properties of a PDR in front of the Trapezium Cluster
• Dicke's Superradiance in Astrophysics. I -- The 21 cm Line
• Herschel CHESS discovery of the fossil cloud that gave birth to the Trapezium and Orion KL
• Merged H/H2 and C+/C/CO transitions in the Orion Bar
• Scattered Nebular Light in the Extended Orion Nebula
• The validity of 21 cm spin temperature as a kinetic temperature indicator in atomic and molecular gas
• Multiline observations of hydrogen, helium, and carbon radio-recombination lines toward Orion A: A detailed dynamical study and direct determination of physical conditions
• Hydrostatic photoionization models of the Orion Bar
• Length-scales and Dynamics of Carina's Western Wall
• Magnetic fields and the location of the PDR
• Large Scale Wind Driven Structures in the Orion Nebula
• Magnetic fields, stellar feedback, and the geometry of H II Regions