Infrared frequencies and intensities for astrophysically important polycyclic aromatic hydrocarbon cations

Szczepański, Jan; Vala, Martin

doi:10.1086/173110

Cited by 150 publications

(147 citation statements)

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“…Note that the flux scales are different for each spectrum (labels on the left for SQ, and on the right for the Galaxy). (Langhoff 1996;Bakes et al 2001a,b;Draine & Li 2001;Bauschlicher 2002) and experimental (e.g., Szczepanski & Vala 1993) studies show that neutral PAHs have lower R 7.7/11.3 μm than charged ones (both anions and cations). The charge state of PAHs is mainly determined by the ionization parameter G UV √ T /n e , where G UV is the integrated far ultraviolet (6−13.6 eV) radiation field expressed in units of the Habing radiation field, T is the electron temperature, and n e is the electronic density.…”

Section: Pah Emission From the Sq Shockmentioning

confidence: 97%

Observations and modeling of the dust emission from the H₂-bright galaxy-wide shock in Stephan's Quintet

Guillard

Boulanger²,

Cluver

et al. 2010

A&A

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Context. Spitzer Space Telescope observations have detected powerful mid-infrared (mid-IR) H 2 rotational line emission from the X-ray emitting large-scale shock (∼15 × 35 kpc 2 ) associated with a galaxy collision in Stephan's Quintet (SQ). Because H 2 forms on dust grains, the presence of H 2 is physically linked to the survival of dust, and we expect some dust emission to originate in the molecular gas. Aims. To test this interpretation, IR observations and dust modeling are used to identify and characterize the thermal dust emission from the shocked molecular gas. Methods. The spatial distribution of the IR emission allows us to isolate the faint PAH and dust continuum emission associated with the molecular gas in the SQ shock. We model the spectral energy distribution (SED) of this emission, and fit it to Spitzer observations. The radiation field is determined with GALEX UV, HST V-band, and ground-based near-IR observations. We consider two limiting cases for the structure of the H 2 gas: it is either diffuse and penetrated by UV radiation, or fragmented into clouds that are optically thick to UV. Results. Faint PAH and dust continuum emission are detected in the SQ shock, outside star-forming regions. The 12/24 μm flux ratio in the shock is remarkably close to that of the diffuse Galactic interstellar medium, leading to a Galactic PAH/VSG abundance ratio. However, the properties of the shock inferred from the PAH emission spectrum differ from those of the Galaxy, which may be indicative of an enhanced fraction of large and neutrals PAHs. In both models (diffuse or clumpy H 2 gas), the IR SED is consistent with the expected emission from dust associated with the warm (>150 K) H 2 gas, heated by a UV radiation field of intensity comparable to that of the solar neighborhood. This is in agreement with GALEX UV observations that show that the intensity of the radiation field in the shock is G UV = 1.4 ± 0.2 [Habing units].Conclusions. The presence of PAHs and dust grains in the high-speed (∼1000 km s −1 ) galaxy collision suggests that dust survives. We propose that the dust that survived destruction was in pre-shock gas at densites higher than a few 0.1 cm −3 , which was not shocked at velocities larger than ∼200 km s −1 . Our model assumes a Galactic dust-to-gas mass ratio and size distribution, and current data do not allow us to identify any significant deviations of the abundances and size distribution of dust grains from those of the Galaxy. Our model calculations show that far-IR Herschel observations will help in constraining the structure of the molecular gas, and the dust size distribution, and thereby to look for signatures of dust processing in the SQ shock.

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Section: Pah Emission From the Sq Shockmentioning

confidence: 97%

Observations and modeling of the dust emission from the H₂-bright galaxy-wide shock in Stephan's Quintet

Guillard

Boulanger²,

Cluver

et al. 2010

A&A

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“…Looking at the spectra, it is clear that there are strong variations in the relative band intensities between the [6−9 µm] and [11−13 µm] ranges. Theoretical (Langhoff 1996 for instance) and laboratory studies (Szczepanski & Vala 1993;Hudgins & Allamandola 1995) have shown that the ratio of the 6.2−"7.7"−8.6 µm to the 11.3−12.7 µm bands increases significantly when PAHs are positively ionized. Using this result, spectrum 1 appears to be dominated by PAH cations and spectrum 2 by PAH neutrals.…”

Section: Molecular Carriersmentioning

confidence: 99%

“…The identification of interstellar PAH species has motivated a wealth of laboratory measurements (Szczepanski & Vala 1993;Hudgins et al 1994Hudgins et al , 1995Kurtz 1993;Joblin et al 1995;Cook et al 1998;Oomens et al 2000;Kim et al 2001 and more recently Banisaukas et al 2004;Mattioda et al 2003;Huneycutt et al 2004). Many quantum chemical calculations have also been performed (de Frees et al 1993;Pauzat et al 1995;Langhoff 1996;Ellinger et al 1999 and more recently Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopy of polycyclic aromatic hydrocarbons and very small grains in photodissociation regions

Rapacioli¹,

Joblin²,

Boissel

2004

A&A

239

299

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Abstract.We have coupled a singular value decomposition method with a Monte Carlo search algorithm to analyse the midinfrared ISOCAM spectral maps of photodissociation regions (PDRs) in NGC 7023 and ρ Oph-SR3.Three different spectra and their associated spatial distribution were extracted from this analysis. It is shown that they can be associated with polycyclic aromatic hydrocarbons (PAHs) in their cationic and neutral forms and a third population of carbonaceous very small grains (VSGs). The method allows for the first time (i) to separate the contribution of neutral PAHs to the interstellar emission spectrum from that of cationic PAHs; (ii) to show that the 7.8 µm component of the "7.7 µm" broad feature is carried by VSGs, whereas the 7.6 µm component is due to PAHs; and (iii) to give evidence that free-flying PAHs are produced in PDRs by photoevaporation of VSGs. It is proposed that these carbonaceous VSGs are indeed PAH clusters. We derived a minimal size of 400 carbon atoms per cluster and estimated a UV absorption power of the order of 10 −24 W C −1 for their dissociation.

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“…Soon after this first PAH cation spectrum, IR matrix isolation spectra of a whole series of cationic PAHs were reported mainly by the Florida (Szczepanski & Vala 1993a) and NASA Ames (Hudgins & Allamandola 1995a,b;Hudgins et al 1994) groups. These spectra provided the first experimental evidence that ionized PAHs may be abundant in the ISM (Allamandola et al 1999;Szczepanski & Vala 1993b).…”

Section: Matrix Isolation Spectroscopymentioning

confidence: 99%

Laboratory infrared spectroscopy of PAHs

Oomens

2011

EAS Publications Series

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Infrared frequencies and intensities for astrophysically important polycyclic aromatic hydrocarbon cations

Cited by 150 publications

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Observations and modeling of the dust emission from the H₂-bright galaxy-wide shock in Stephan's Quintet

Observations and modeling of the dust emission from the H₂-bright galaxy-wide shock in Stephan's Quintet

Spectroscopy of polycyclic aromatic hydrocarbons and very small grains in photodissociation regions

Laboratory infrared spectroscopy of PAHs

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Infrared frequencies and intensities for astrophysically important polycyclic aromatic hydrocarbon cations

Cited by 150 publications

References 0 publications

Observations and modeling of the dust emission from the H2-bright galaxy-wide shock in Stephan's Quintet

Observations and modeling of the dust emission from the H2-bright galaxy-wide shock in Stephan's Quintet

Spectroscopy of polycyclic aromatic hydrocarbons and very small grains in photodissociation regions

Laboratory infrared spectroscopy of PAHs

Contact Info

Product

Resources

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Observations and modeling of the dust emission from the H₂-bright galaxy-wide shock in Stephan's Quintet

Observations and modeling of the dust emission from the H₂-bright galaxy-wide shock in Stephan's Quintet