Far-ultraviolet Dust Extinction and Molecular Hydrogen in the Diffuse Milky Way Interstellar Medium

Abstract

We aim to compare variations in the full-UV dust extinction curve (912-3000 Angstrom), with the HI/H${}_2$/total H content along diffuse Milky Way sightlines, to investigate possible connections between ISM conditions and dust properties. We combine an existing sample of 75 UV extinction curves based on IUE and FUSE data, with atomic and molecular column densities measured through UV absorption. The H${}_2$ column density data are based on existing Lyman-Werner absorption band models from earlier work on the extinction curves. Literature values for the HI column density were compiled, and improved for 23 stars by fitting a Ly$\alpha$ profile to archived spectra. We discover a strong correlation between the H${}_2$ column and the far-UV extinction, and the underlying cause is a linear relationship between H${}_2$ and the strength of the far-UV rise feature. This extinction does not scale with HI, and the total H column scales best with $A(V)$ instead. The carrier of the far-UV rise therefore coincides with molecular gas, and further connections are shown by comparing the UV extinction features to the molecular fraction. Variations in the gas-to-extinction ratio $N(\mathrm{H})/A(\mathrm{V})$ correlate with the UV-to-optical extinction ratio, and we speculate this could be due to coagulation or shattering effects. Based on the H${}_2$ temperature, the strongest far-UV rise strengths are found to appear in colder and denser sightlines.

arXiv comment24 pages, 9 figures, accepted for publication in ApJ; fix missing text in generated pdf due to broken tex command

References in corpus (64)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• The Relation Between Optical Extinction and Hydrogen Column Density in the Galaxy
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point
• A PDR-Code Comparison Study
• Evolution of interstellar dust and stardust in the solar neighbourhood
• A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
• Dust coagulation and fragmentation in molecular clouds. I. How collisions between dust aggregates alter the dust size distribution
• Molecular Hydrogen in the FUSE Translucent Lines of Sight: The Full Sample
• Starburst-like Dust Extinction in the Small Magellanic Cloud
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds
• Ultraviolet Extinction Properties in the Milky Way
• A Reanalysis of theUltraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud
• Dust Formation in Milky Way-like Galaxies
• The Dust Budget of the SMC: Are AGB Stars the Primary Dust Source at Low Metallicity?
• FUSE Measurements of Far-Ultraviolet Extinction. III. The Dependence on R(V) and Discrete Feature Limits from 75 Galactic Sightlines
• What determines the grain size distribution in galaxies?
• Modelling Dust Evolution in Galaxies with a Multiphase, Inhomogeneous ISM
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. II. Gas-to-Dust Ratio Variations across ISM Phases
• The Spitzer Survey of the Small Magellanic Cloud (S3MC): Insights into the Life-Cycle of Polycyclic Aromatic Hydrocarbons
• Direct evidence of dust growth in L183 from MIR light scattering
• The dust budget crisis in high-redshift submillimetre galaxies
• The gas-to-extinction ratio and the gas distribution in the Galaxy
• Dust growth in the interstellar medium: How do accretion and coagulation interplay?
• Hyper-Fit: Fitting Linear Models to Multidimensional Data with Multivariate Gaussian Uncertainties
• Surface chemistry in the Interstellar Medium II. ${\mathrm{H}}_2$ formation on dust with random temperature fluctuations
• The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
• Electronic spectroscopy of medium-sized polycyclic aromatic hydrocarbons: Implications for the carriers of the 2175 Å UV bump
• The penetration of FUV radiation into molecular clouds
• FUSE Measurements of Far Ultraviolet Extinction. II. Magellanic Cloud Sight Lines
• Optical-NIR dust extinction towards Galactic O stars
• Remodeling the evolution of grain size distribution in galaxies
• Interstellar Gas-phase Element Depletions in the Small Magellanic Cloud: A Guide to Correcting for Dust in QSO Absorption Line Systems
• FUSE Observations of Molecular Hydrogen in Translucent Interstellar Clouds: II. The Line of Sight Toward HD 110432
• Elemental depletions in the Magellanic Clouds and the evolution of depletions with metallicity
• Galaxy simulation with the evolution of grain size distribution
• H2 formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen
• Evolution of dust extinction curves in galaxy simulation
• A Far Ultraviolet Spectroscopic Explorer Survey of Interstellar Molecular Hydrogen in the Galactic Disk
• Evolution of the extinction curves in galaxies
• METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble program. II. Variations of interstellar depletions and dust-to-gas ratio within the LMC
• METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble program. I. Overview and Initial Results
• Dust Abundance Variations in the Magellanic Clouds: Probing the Lifecycle of Metals with All-Sky Surveys
• FUSE Measurements of Far Ultraviolet Extinction. I. Galactic Sight Lines
• Polycyclic Aromatic Hydrocarbons, the Anomalous Microwave Emission, and Their Connection to the Cold Neutral Medium
• Photoinduced polycyclic aromatic hydrocarbon dehydrogenation: Molecular hydrogen formation in dense PDRs
• Observational Evidence Linking Interstellar UV Absorption to PAH Molecules
• H2 formation via the UV photo-processing of a-C:H nano-particles
• The co-evolution of molecular hydrogen and the grain size distribution in an isolated galaxy
• Large Interstellar Polarisation Survey II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM
• Evolution of the grain size distribution in galactic discs
• The smoothness of the interstellar extinction curve in the UV. Comparison with recent laboratory measurements of PAH mixtures
• Relations between mid-IR dust emission and UV extinction
• Evidence of dust grain evolution from extinction mapping in the IC 63 photodissociation region
• Interstellar Extinction and Elemental Abundances: Individual Sight Lines
• The effect of grain size distribution on H${}_2$ formation rate in the interstellar medium
• UV Extinction as a More Fundamental Measure of Dust than E(B-V) or A(V)
• On the Correlation Between CO Absorption and Far-Ultraviolet Non-Linear Extinction Toward Galactic OB Stars

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