AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82

Yamagishi, Masao; Kaneda, Hidehiro; Ishihara, Daisuke; Kondô, Torû; Onaka, Takashi; Suzuki, Toyoaki; Minh, Young Chol

doi:10.1051/0004-6361/201218904

Cited by 47 publications

(51 citation statements)

References 34 publications

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“…1 schematic view), as predicted by Jones (2012c) and Jones et al (2013), comes from the observed 3−4 μm region emission band spectra in many sources, e.g., NGC 7023 (Pilleri et al 2015), the Orion Bar (Sloan et al 1997;Verstraete et al 2001), M17 SW, NGC 2023 (Verstraete et al 2001), M 82 (Yamagishi et al 2012) and the Seyfert 1 galaxy NGC 1097 (Kondo et al 2012). Even in these energetic regions the 3.3 μm aromatic CH band always appears to be accompanied by a CH n aliphatic plateau in the 3.4−3.6 μm region.…”

Section: Introductionmentioning

confidence: 80%

H₂formation via the UV photo-processing of a-C:H nano-particles

Jones

Habart

2015

A&A

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Context. The photolysis of hydrogenated amorphous carbon, a-C(:H), dust by UV photon-irradiation in the laboratory leads to the release of H 2 as well as other molecules and radicals. This same process is also likely to be important in the interstellar medium. Aims. We investigate molecule formation arising from the photo-dissociatively-driven, regenerative processing of a-C(:H) dust. Methods. We explore the mechanism of a-C(:H) grain photolysis leading to the formation of H 2 and other molecules/radicals. Results. The rate constant for the photon-driven formation of H 2 from a-C(:H) grains is estimated to be 2 × 10 −17 cm 3 s −1 . In intense radiation fields photon-driven grain decomposition will lead to fragmentation into daughter species rather than H 2 formation. Conclusions. The cyclic re-structuring of arophatic a-C(:H) nano-particles appears to be a viable route to formation of H 2 for low to moderate radiation field intensities (1 < ∼ G 0 < ∼ 10 2 ), even when the dust is warm (T ∼ 50−100 K).

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Section: Introductionmentioning

confidence: 80%

H₂formation via the UV photo-processing of a-C:H nano-particles

Jones

Habart

2015

A&A

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“…Thus, the optEC (s) (a) model then also predicts that no IR emission band spectrum, arising from hydro-carbonaceous dust, and exhibiting only a 3.28 μm aromatic CH band, in the 3 μm region will be observable in the ISM. Some evidence that seems to support this prediction, and therefore favour an a-C(:H) origin for the IR emission bands, comes from AKARI observations of the IR emission features in M 82, which show no pure aromatic CH band but only aromatic and aliphatic CH bands that always appear together, even in the very energetic superwind region (Yamagishi et al 2012). In contrast, the PAH and (surface-hydrogenated) graphitic interstellar dust models both, implicitly, allow for the possibility of a "pure" 3.28 μm aromatic CH emission band in the 3 μm region, which is apparently never observed.…”

Section: Structural Variations and Spectral Propertiesmentioning

confidence: 94%

Variations on a theme – the evolution of hydrocarbon solids

Jones

2012

A&A

102

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Context. The properties of hydrogenated amorphous carbon (a-C:H) dust evolve in response to the local radiation field in the interstellar medium (ISM) and the evolution of these properties is particularly dependent upon the particle size. Aims. A model for finite-sized, low-temperature amorphous hydrocarbon particles, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, with surfaces passivated by hydrogen atoms, has been developed. Methods. The eRCN/DG and the optEC (s) models have been combined, adapted and extended into a new optEC (s) (a) model that is used to calculate the optical properties of hydrocarbon grain materials down into the sub-nanometre size regime, where the particles contain only a few tens of carbon atoms. Results. The optEC (s) (a) model predicts a continuity in properties from large to small (sub-nm) carbonaceous grains. Tabulated data of the size-dependent optical constants (from EUV to cm wavelengths) for a-C:H (nano-)particles as a function of the bulk material band gap [E g (bulk)], or equivalently the hydrogen content, are provided. The effective band gap [E g (eff.)] is found to be significantly larger than E g (bulk) for hydrogen-poor a-C(:H) nano-particles and their predicted long-wavelength (λ > 30 μm) optical properties differ from those derived for interstellar polycyclic aromatic hydrocarbons (PAHs). Conclusions. The optEC (s) (a) model is used to investigate the size-dependent structural and spectral evolution of a-C(:H) materials under ISM conditions, including: the IR-FUV extinction, the 217 nm bump and the infrared emission bands. The model makes several predictions that can be tested against observations.

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“…This confirms the need for non-zero offset in intensity scaling because f ali = f aro . Nagata et al 1988), (e) IRAS 04296+3429 (protoplanetary nebula, Geballe et al 1992), (f) CRL 2688 (protoplanetary nebula, Geballe et al 1992), (g) HD 34700 (debris disk, Smith et al 2004), (h) M 82 (starburst galaxy, Yamagishi et al 2012), and (i) four methylated PAH molecules. Intensities calculated at B3LYP vs. MP2 with the same basis set.…”

Section: A Rationale For a Non-zero Offset In The Intensity Scaling mentioning

confidence: 99%

Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups: Intensity Scaling for the C–H Stretching Modes and Astrophysical Implications

Yang

Glaser

et al. 2017

ApJ

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The so-called unidentified infrared emission (UIE) features at 3. 3, 6.2, 7.7, 8.6, and 11.3 µm ubiquitously seen in a wide variety of astrophysical regions are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. Astronomical PAHs may have an aliphatic component as revealed by the detection in many UIE sources of the aliphatic C-H stretching feature at 3.4 µm. The ratio of the observed intensity of the 3.4 µm feature to that of the 3.3 µm aromatic C-H feature allows one to estimate the aliphatic fraction of the UIE carriers. This requires the knowledge of the intrinsic oscillator strengths of the 3.3 µm aromatic C-H stretch (A 3.3 ) and the 3.4 µm aliphatic C-H stretch (A 3.4 ). Lacking experimental data on A 3.3 and A 3.4 for the UIE candidate materials, one often has to rely on quantum-chemical computations. Although the second-order Møller-Plesset (MP2) perturbation theory with a large basis set is more accurate than the B3LYP density functional theory, MP2 is computationally very demanding and impractical for large molecules. Based on methylated PAHs, we show here that, by scaling the band strengths computed at an inexpensive level (e.g., B3LYP/6-31G * ) we are able to obtain band strengths as accurate as that computed at far more expensive levels (e.g., MP2/6-311+G(3df,3pd)). We calculate the model spectra of methylated PAHs and their cations excited by starlight of different spectral shapes and intensities. We find (I 3.4 /I 3.3 ) mod , the ratio of the model intensity of the 3.4 µm feature to that of the 3.3 µm feature, is insensitive to the spectral shape and intensity of the exciting starlight. We derive a straightforward relation for determining the aliphatic fraction of the UIE carriers (i.e., the ratio of the number of C atoms in aliphatic units N C,ali to that in aromatic rings N C,aro ) from the observed band ratios (I 3.4 /I 3.3 ) obs : N C,ali /N C,aro ≈ 0.57 × (I 3.4 /I 3.3 ) obs for neutrals and N C,ali /N C,aro ≈ 0.26 × (I 3.4 /I 3.3 ) obs for cations.

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AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82

Cited by 47 publications

References 34 publications

H₂formation via the UV photo-processing of a-C:H nano-particles

H₂formation via the UV photo-processing of a-C:H nano-particles

Variations on a theme – the evolution of hydrocarbon solids

Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups: Intensity Scaling for the C–H Stretching Modes and Astrophysical Implications

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AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82

Cited by 47 publications

References 34 publications

H2formation via the UV photo-processing of a-C:H nano-particles

H2formation via the UV photo-processing of a-C:H nano-particles

Variations on a theme – the evolution of hydrocarbon solids

Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups: Intensity Scaling for the C–H Stretching Modes and Astrophysical Implications

Contact Info

Product

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H₂formation via the UV photo-processing of a-C:H nano-particles

H₂formation via the UV photo-processing of a-C:H nano-particles