Vibrationally Excited Molecular Hydrogen Near Herschel 36

Abstract

We present the first high resolution UV spectra toward Herschel 36, a Trapezium-like system of high-mass stars contained within the Lagoon Nebula (M8, NGC 6523). The spectra reveal extreme ro-vibrational excitation of molecular hydrogen in material at a single velocity or very small range of velocities, with this component presumably lying near the star system and undergoing fluorescent excitation. The overall H${}_2$ excitation is similar to, but apparently larger than, that seen towards HD 37903 which previously showed the largest vibrationally excited H${}_2$ column densities seen in UV absorption spectra. While the velocities of the highly excited H${}_2$ lines are consistent within each observation, it appears that they underwent a $\sim$60 km s${}^{-1}$ redshift during the 3.6 years between observations. In neither case does the velocity of the highly excited material match the velocity of the bulk of the line-of-sight material which appears to mostly be in the foreground of M8. Recent work shows unusually excited CH and CH${}^{+}$ lines and several unusually broad Diffuse Interstellar Bands towards Herschel 36. Along with the H${}_2$ excitation, all of these findings appear to be related to the extreme environment within $\sim$0.1 pc of the massive young stellar system.

arXiv comment11 pages, 11 figures, accepted for publication in ApJ

References in corpus (20)

• An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology
• Overview of the Far Ultraviolet Spectroscopic Explorer Mission
• A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
• Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
• Molecular Hydrogen in the FUSE Translucent Lines of Sight: The Full Sample
• Abundances and Behavior of 12CO, 13CO, and C2 in Translucent Sight Lines
• Direct Measurement of the Ratio of Carbon Monoxide to Molecular Hydrogen in the Diffuse Interstellar Medium
• CalFUSE v3: A Data-Reduction Pipeline for the Far Ultraviolet Spectroscopic Explorer
• Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36. II. Analysis of Radiatively Excited CH+, CH, and DIBs
• Molecular Hydrogen in the Direction of zeta Ori A
• Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36. I. Observations of Rotationally Excited CH and CH+ Absorption and Strong, Extended Redward Wings on Several DIBs
• Velocity Dispersion of Excited H2
• A far UV study of interstellar gas towards HD34078: high excitation H2 and small scale structure - Based on observations performed by the FUSE mission and at the CFHT telescope
• High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments
• On the multiplicity of the zero-age main-sequence O star Herschel 36
• Observational Properties of Rotationally Excited Molecular Hydrogen In Translucent Lines of Sight
• CO emission and variable CH and CH+ absorption towards HD34078: evidence for a nascent bow shock ?
• Interstellar H2 toward HD 37903
• Interstellar H2 toward HD 147888
• Molecular Hydrogen in the Lagoon: H2 line emission from Messier 8

Cited by in corpus (4)

• Interstellar Hydrides
• The Behavior of Selected Diffuse Interstellar Bands with Molecular Fraction in Diffuse Atomic and Molecular Clouds
• Formation of ${\text{H}}_2$ on polycyclic aromatic hydrocarbons under conditions of the ISM: an ab initio molecular dynamics study
• The EDIBLES survey. X. The 6196 Å diffuse interstellar band: Identification of side DIBs as an indication of a small carrier molecule