Unidentified infrared bands in the interstellar medium across the Galaxy

Kahanpää, Jere; Mattila, K.; Lehtinen, K.; Leinert, Christoph; Lemke, D.

doi:10.1051/0004-6361:20030440

Cited by 39 publications

(49 citation statements)

References 28 publications

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“…Simpson et al (1998);6 : Roelfsema et al (1996); 7 : Verstraete et al (1996); 8 : Henning et al (1998);9 : Moutou et al (1999a); 10 : Moutou et al (1999b);11 : Gerakines et al (1999);12 : Lutz et al (1996) 13 : Lutz et al (1999) 14 : Boulanger et al (1996 15 : Kahanpää et al (2003);16 : Reach et al (2000); 17 : Onaka et al (1996); 18 : Vermeij et al (2002);19 : Werner et al (1976);20 : Thronson et al (1984); 21 : Meixner et al (1992);22 : Casey (1991);23 : Steiman-Cameron et al (1997);24 : Thronson & Harper (1979) …”

Section: Galactic Sampleunclassified

Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?

Peeters

Spoon

Tielens

2004

ApJ

394

487

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Infrared (IR) emission features at 3. 3, 6.2, 7.7, 8.6 and 11.3 µm are generally attributed to IR fluorescence from (mainly) FUV pumped large Polycyclic Aromatic Hydrocarbon (PAH) molecules. As such, these features trace the FUV stellar flux and are thus a measure of star formation. We examined the IR spectral characteristics of Galactic massive star forming regions and of normal and starburst galaxies, as well as AGNs and ULIRGs. The goal of this study is to analyze if PAH features are a good qualitative and/or quantitative tracer of star formation and hence the application of PAH emission as a diagnostic tool in order to identify the dominant processes contributing to the infrared emission from Seyfert's and ULIRGs. We develop a new MIR/FIR diagnostic diagram based upon our Galactic sample and compare it to the diagnostic tools of Genzel et al. (1998) and(Laurent et al. 2000), with these diagnostic tools also applied to our Galactic sample. This MIR/FIR diagnostic is derived from the FIR normalized 6.2 µm PAH flux and the FIR normalized 6.2 µm continuum flux. Within this diagram, the Galactic sources form a sequence spanning a range of 3 orders of magnitude in these ratios, ranging from embedded compact H II regions to exposed Photo Dissociation Regions (PDRs) and the (diffuse) ISM. However, the variation in the 6.2 µm PAH feature-to-continuum ratio is relative small. Comparison -2 -of our extragalactic sample with our Galactic sources revealed an excellent resemblance of normal and starburst galaxies to exposed PDRs. While Seyfert-2's coincide with the starburst trend, Seyfert-1's are displaced by at least a factor 10 in 6.2 µm continuum flux, in accordance with general orientation dependent unification schemes for AGNs. ULIRGs show a diverse spectral appearance. Some show a typical AGN hot dust continuum. More, however, are either starburstlike or show signs of strong dust obscuration in the nucleus. One characteristic of the ULIRGs also seems to be the presence of more prominent FIR emission than either starburst galaxies or AGNs. We discuss the observed variation in the Galactic sample in view of the evolutionary state and the PAH/dust abundance and discuss the use of PAHs as quantitative tracers of star formation activity. Based on these investigations we find that PAHs may be better suited as a tracer of B stars, which dominate the Galactic stellar energy budget, than as a tracer of massive star formation (O stars).

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Section: Galactic Sampleunclassified

Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?

Peeters

Spoon

Tielens

2004

ApJ

394

487

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“…The fact that the bands are detected far from any illuminating source with roughly the same intensity ratios as those close to bright stars proves that the carriers are excited nonthermally by single UV photons (Sellgren 1984) and are interstellar. Indeed, both CAM-CVF and PHOT-S as well as the IRTS have shown that the mid-IR spectra (and thus also the IRAS 12 µm emission) of even the most diffuse interstellar medium are dominated by PAH features (Mattila et al 1996, Onaka et al 1996, Boulanger et al 2000, Kahanpää et al 2003. Any large (>100Å) grain does not become hot enough under these conditions to emit at mid-IR wavelengths, so the carriers must be small, of order 10Å, and correspond to PAHs with 30 to a few hundred carbon atoms containing up to 10-15% of the available interstellar carbon.…”

Section: Polycyclic Aromatic Hydrocarbonsmentioning

confidence: 99%

ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks

Dishoeck

2004

Annu. Rev. Astron. Astrophys.

264

148

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■ Abstract Observations of interstellar gas-phase and solid-state species in the 2.4-200 µm range obtained with the spectrometers on board the Infrared Space Observatory (ISO) are reviewed. Lines and bands caused by ices, polycyclic aromatic hydrocarbons, silicates, and gas-phase atoms and molecules (in particular H 2 , CO, H 2 O, OH, and CO 2 ) are summarized and their diagnostic capabilities illustrated. The results are discussed in the context of the physical and chemical evolution of starforming regions, including photon-dominated regions, shocks, protostellar envelopes, and disks around young stars.

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“…The origin of the difference between class A and B objects may be attributed to the inclusion of hetero atoms (Peeters et al 2002) or carbon isotopes in the band carriers (Wada et al 2003). On the other hand, the UIR band spectrum observed in the diffuse Galactic radiation does not exhibit any systematic variations in the inner part of the Galaxy (Chan et al 2001;Kahanpää et al 2003), whereas Sakon et al (2004) detected small variations in the band ratio and the peak wavelength between the inner part of the Galaxy and the outer part. Variations in the band spectra of external galaxies and within a given galaxy are also generally small (e.g., Smith et al 2007a;Gordon et al 2008).…”

Section: Introductionmentioning

confidence: 90%

Detection of unidentified infrared bands in a Hαfilament in the dwarf galaxy NGC 1569 with AKARI

Onaka

Matsumoto

Sakon

et al. 2010

A&A

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Context. We report the detection of unidentified infrared (UIR) bands in a filamentary structure associated with Hα emission in the starburst dwarf galaxy NGC 1569 based on imaging and spectroscopic observations of the AKARI satellite. Aims. We investigate the processing and destruction of the UIR band carriers in an outflow from NGC 1569. Methods. We performed observations of NGC 1569 for 6 infrared bands (3.2, 4.1, 7, 11, 15, and 24 μm) with the infrared camera (IRC) onboard AKARI. Near-to mid-infrared (2−13 μm) spectroscopy of a Hα filament was also carried out with the IRC. Results. The extended structure associated with a Hα filament appears bright at 7 μm. Since the IRC 7 μm band (S7) efficiently traces the 6.2 and 7.7 μm UIR band emission, the IRC imaging observations suggest that the filament is bright at the UIR band emission. Follow-up spectroscopic observations with the IRC confirm the presence of 6.2, 7.7, and 11.3 μm emission in the filament. The filament spectrum exhibits strong 11.3 μm UIR band emission relative to the 7.7 μm band compared to the galaxy disk observed with the infrared spectrograph on Spitzer. The near-infrared spectrum also suggests the presence of excess continuum emission in 2.5−5 μm in the filament. Conclusions. The presence of the UIR bands associated with a Hα filament is found by AKARI/IRC observations. The Hα filament is thought to have been formed by the galactic outflow originating from the star-formation activity in the disk of NGC 1569. The destruction timescale of the UIR band carriers in the outflow is estimated to be much shorter (∼1.3 × 10 3 yr) than the timescale of the outflow (∼5.3 Myr). Thus it is unlikely that the band carriers survive the outflow environment. Alternatively, we suggest that the band carriers in the filaments may be produced by the fragmentation of large carbonaceous grains in shocks, which produce the Hα emission. The NIR excess continuum emission cannot be accounted for by free-free emission alone and a hot dust contribution may be needed, although the free-free emission intensity estimated from H i recombination lines has a large uncertainty.

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Unidentified infrared bands in the interstellar medium across the Galaxy

Cited by 39 publications

References 28 publications

Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?

Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?

ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks

Detection of unidentified infrared bands in a Hαfilament in the dwarf galaxy NGC 1569 with AKARI

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