Raman mapping of photodissociation regions

Abstract

Broad Raman-scattered wings of hydrogen lines can be used to map neutral gas illuminated by high-mass stars in star forming regions. Raman scattering transforms far-ultraviolet starlight from the wings of the Lyman beta line (1022 Angstrom to 1029 Angstrom) to red visual light in the wings of the H alpha line (6400 Angstrom to 6700 Angstrom). Analysis of spatially resolved spectra of the Orion Bar and other regions in the Orion Nebula shows that this process occurs in the neutral photo-dissociation region between the ionization front and dissociation front. The inner Raman wings are optically thick and allow the neutral hydrogen density to be determined, implying n(H0) ~= 100,000 per cubic cm for the Orion Bar. Far-ultraviolet resonance lines of neutral oxygen imprint their absorption onto the stellar continuum as it passes through the ionization front, producing characteristic absorption lines at 6633 Angstrom and 6664 Angstrom with widths of order 2 Angstrom. This is a unique signature of Raman scattering, which allows it to be easily distinguished from other processes that might produce broad H alpha wings, such as electron scattering or high-velocity outflows.

19 pages. Submitted to MNRAS

References in corpus (17)

• The MUSE second-generation VLT instrument
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• A Catalog of Diffuse Interstellar Bands in the Spectrum of HD 204827
• The Gould's Belt Distances Survey (GOBELINS) II. Distances and structure towards the Orion Molecular Clouds
• Confirming interstellar C${}_{60}^{+}$ using the Hubble Space Telescope
• Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
• Flux calibration of medium-resolution spectra from 300 nm to 2500 nm: Model reference spectra and telluric correction
• MONOS: Multiplicity Of Northern O-type Spectroscopic systems. I. Project description and spectral classifications and visual multiplicity of previously known objects
• A Multi-Color Optical Survey of the Orion Nebula Cluster. Part I: the Catalog
• Skycorr: A general tool for spectroscopic sky subtraction
• The Orion HII Region and the Orion Bar in the Mid-Infrared
• Deviations from He I Case B Recombination Theory and Extinction Corrections in the Orion Nebula
• Polyacenes and diffuse interstellar bands
• Dusting off the diffuse interstellar bands: DIBs and dust in extragalactic SDSS spectra
• Structure and Physical Conditions in the Huygens Region of the Orion Nebula
• Extended Red Emission in IC59 and IC63
• Are the Carriers of Diffuse Interstellar Bands and Extended Red Emission the same?

Cited by in corpus (9)

• PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
• PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
• Challenging the AGN scenario for JWST/NIRSpec LRD and non-LRD broad H$\alpha$ emitters in light of non-detection of NIRCam photometric variability and X-ray
• PDRs4All. X. ALMA and JWST detection of neutral carbon in the externally irradiated disk d203-506: Undepleted gas-phase carbon
• Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots
• Rayleigh and Raman scattering cross-sections and phase matrices of the ground-state hydrogen atom, and their astrophysical implications
• An episodically variable stellar wind in the planetary nebula IC\,4997
• PDRs4All. V. Modelling the dust evolution across the illuminated edge of the Orion Bar
• Low-ionization structures in planetary nebulae -- IV. The molecular hydrogen counterpart