Polycyclic Aromatic Hydrocarbon Emission in the 15-21 Micron Region

Peeters, E.; Mattioda, A. L.; Hudgins, Douglas M.; Allamandola, Louis J.

doi:10.1086/427186

Cited by 102 publications

(116 citation statements)

References 24 publications

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“…Furthermore, the 15−20 μm region is more crowded with bands when a strong 17.4 μm band is present. Second, the 16.4 μm band tends to be associated with pendent hexagonal rings, consistent with the conclusions by Peeters et al (2004) and the discussion in Sect. 3.2.…”

Section: "Blind" Searchsupporting

confidence: 89%

“…No clear relationship could be identified for the other bands between 15−20 μm with any of the PAH bands (6.2, "7.7", 11.2 and 12.7 μm), although sometimes those were limited by the number of data points. Peeters et al (2004) have investigated the relation between the 15−20 μm bands and the mid-IR PAH band classification. Specifically, the "7.7" μm band was classified as A, B or C depending on the peak position of this band.…”

Section: The 15-20 μM Featuresmentioning

confidence: 99%

“…With the arrival of the NASA Spitzer Space Telescope (Werner et al 2004a) and its unprecedented sensitivity, these and other new sub-features are now reported routinely and can be studied systematically. Peeters et al (2004) make a comparison between the early Spitzer data and ISO-SWS spectra and are able to infer that the sources that show a clear 17.4 μm feature also possess a relatively strong 16.4 μm feature. The classes as defined by Peeters et al (2002) and van Diedenhoven et al (2004) -on the basis of the spectral variations in the 3−15 μm region -do not appear to correlate strongly with the variations in the emission between 15−20 μm.…”

Section: Introductionmentioning

confidence: 99%

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The 15–20 μm PAH emission features: probes of individual PAHs?

Boersma¹,

Bauschlicher

Allamandola

et al. 2010

A&A

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124

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Context. Spectral features between about 15−20 μm are commonly associated with polycyclic aromatic hydrocarbons (PAHs). With the NASA Spitzer Space Telescope these features are reported routinely, and as such, warrant a deeper molecular explanation. Aims. We aim to determine the characteristics of the group of carriers of the plateau and the distinct sub-features at 15.8, 16.4, 17.4, 17.8 and 18.9 μm and to draw astronomical implications from these spectra. Methods. We analyse and interpret the spectra of 15 different sources using the NASA Ames PAH IR spectroscopic database. Results. The bands within the 15−20 μm region show large variations. Except for the 16.4 μm band, there is also no connection, both in band strength and feature classification, with the mid-IR PAH bands. Of the PAH spectra considered, only those from species containing pendent rings show one "common" characteristic: a band near the astronomical 16.4 μm position. However, coupling with the carbon skeleton's core influences its precise position in the spectrum. Compact PAHs in the size range 50−130 carbon atoms, consistently show a strong band near the astronomical 17.4 μm band position. Conclusions. The 15−20 μm region is the transition zone from PAH nearest neighbour modes to full-skeleton modes. We conclude that a few individual PAHs dominate the astronomical PAH family when clear features are prominent. In the few cases of a broad plateau, the PAH family would be far richer. Although PAHs containing pendent rings showed promise explaining the astronomical 16.4 μm band, coupling with the skeleton core and the inherent strong quartet mode expected around 13.5 μm, make it a less viable candidate. The number of large PAHs in the database becomes a limitation in studying the emission between 15−20 μm and longward. Computation of larger PAH spectra should therefore be stimulated, especially for understanding the forthcoming far-IR data expected from Herschel, SOFIA and ALMA.

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Section: "Blind" Searchsupporting

confidence: 89%

Section: The 15-20 μM Featuresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The 15–20 μm PAH emission features: probes of individual PAHs?

Boersma¹,

Bauschlicher

Allamandola

et al. 2010

A&A

Self Cite

124

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“…Peeters et al 2004). This well-established correlation has led to the use of PAH strength as a tracer of star formation (e.g.…”

Section: Pah Featuresmentioning

confidence: 99%

Nuclear obscuration in LINERs

González‐Martín

Masegosa

Márquez

et al. 2015

A&A

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Context. Most of the optically classified low-ionisation, narrow emission-line regions (LINERs) nuclei host an active galactic nucleus (AGN). However, how they fit into the unified model (UM) of AGN is still an open question.Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e. hydrogen column densities of N H > 1.5 × 10 24 cm −2 ) and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral-resolution, mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PG QSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and StarBurst (SB) nuclei. We studied the AGN compared to the starburst content in our sample using different indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 µm, the strength of the silicate feature at 9.7 µm, and the steepness of the mid-IR spectra. We classified the spectra as SB-dominated and AGN-dominated, according to these diagnostics and compared the average mid-IR spectra of the various classes. Moreover, we studied the correlation between the 12 µm luminosity, νL ν (12 µm), and the 2−10 keV energy band X-ray luminosity, L X (2−10 keV). Results. In 25 out of the 40 LINERs (i.e. 62.5%), the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is different from the average spectra of the other optical classes, showing a rather flat spectrum at 6−28 µm. We find that the average spectrum of AGN-dominated LINERs with X-ray luminosities L X (2−10 keV) > 10 41 erg/s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. L X (2−10 keV) < 10 41 erg/s) show flat spectra different from any of the other optical classes. The correlation between νL ν (12 µm) and L X (2−10 keV) for AGN nicely extends towards low luminosities only if SB-dominated LINERs are excluded and if the 2−10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We find that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence that the dusty-torus disappear when their bolometric luminosity is below L bol 10 42 erg/s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. To reconcile the Compton-thick nature of a large number of LINERs without dusty-torus signatures, we suggest that the material producing the ...

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“…PDR) and the ionised medium. To validate its use as a star formation indicator, it is interesting to compare the [CII] emission with other known tracers of the star formation process, such as PAHs (Peeters et al 2004). In and 145 μm lines behind the PDR, and a more parabolic relationship in front of it.…”

Section: Comparison With Co H 2 and Pah Emissionmentioning

confidence: 99%

Spatial variation of the cooling lines in the reflection nebula NGC 7023

Bernard─Salas

Habart

Koehler

et al. 2015

A&A

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Context. The north-west photo-dissociation region (PDR) in the reflection nebula NGC 7023 displays a complex structure. Filamentlike condensations at the edge of the cloud can be traced via the emission of the main cooling lines, offering a great opportunity to study the link between the morphology and energetics of these regions.Aims. We study the spatial variation of the far-infrared fine-structure lines of [C ii] (158 μm) and [O i] (63 and 145 μm). These lines trace the local gas conditions across the PDR. We also compare their emission with molecular tracers including rotational and rovibrational lines of H 2 and high-rotational lines of CO. Methods. We used observations from the Herschel/PACS instrument to map the spatial distribution of these fine-structure lines. The observed region covers a square area of about 110 × 110 with an angular resolution that varies from 4 to 11 . We compared this emission with ground-based and Spitzer observations of H 2 lines, Herschel/SPIRE observations of CO lines, and Spitzer/IRAC 3.6 μm images that trace the emission of polycyclic aromatic hydrocarbons. We have tested whether the density profile and peak densities that were derived in previous studies to model the dust and molecular emission can predict the [O i]145 μm emission. We find that the model with a peak density of 10 6 cm −3 , and 2 × 10 4−5 cm −3 in the oxygen emitting region predicts an [O i]145 μm line that is only 30% lower than the observed emission. Finally, we did not detect emission from [N ii]122 μm, suggesting that the cavity is mostly filled with non-ionised gas.

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Polycyclic Aromatic Hydrocarbon Emission in the 15-21 Micron Region

Cited by 102 publications

References 24 publications

The 15–20 μm PAH emission features: probes of individual PAHs?

The 15–20 μm PAH emission features: probes of individual PAHs?

Nuclear obscuration in LINERs

Spatial variation of the cooling lines in the reflection nebula NGC 7023

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