Variations of the Mid-IR Aromatic Features inside and among Galaxies

By F. Galliano, S. Madden, A. Tielens, E. Peeters, A. Jones. 2008

227 citations recorded by the source corpus.

We present the results of a systematic study of mid-IR spectra of Galactic regions, Magellanic H II regions, and galaxies of various types (dwarf, spiral, starburst), observed by the satellites ISO and Spitzer. We study the relative variations of the 6.2, 7.7, 8.6, and 11.3 μm features inside spatially resolved objects (such as M82, M51, 30 Doradus, M17, and the Orion Bar), as well as among 90 integrated spectra of 50 objects. Our main results are that the 6.2, 7.7, and 8.6 μm bands are essentially tied together, while the ratios between these bands and the 11.3 μm band vary by 1 order of magnitude. This implies that the properties of the PAHs are remarkably universal throughout our sample and that the relative variations of the band ratios are mainly controlled by the fraction of ionized PAHs. In particular, we show that we can rule out both the modification of the PAH size distribution and the mid-IR extinction as an explanation of these variations. Using a few well-studied Galactic regions (including the spectral image of the Orion Bar), we give an empirical relation between the I6.2/I11.3 ratio and the ionization/recombination ratio G0/neT1/2gas, therefore providing a useful quantitative diagnostic tool of the physical conditions in the regions where the PAH emission originates. Finally, we discuss the physical interpretation of the I6.2/I11.3 ratio, on galactic size scales.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/4a2c4f86f8bb5e563408d7936be60986f653bf8d

How researchers see this paper

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In Astronomy and Astrophysics

1. D. M. Alexander
2. R. Ivison
3. I. Smail
4. S. Chapman
5. A. Blain
6. Lee Armus
7. C. Casey
8. D. Narayanan

In Spectroscopy

1. S. Chapman
2. E. Peeters
3. A. Blain
4. L. Allamandola
5. R. Ivison
6. C. Bauschlicher
7. F. Galliano
8. France.

Citations in the corpus

• Non-standard grain properties, dark gas reservoir, and extended submillimeter excess, probed by Herschel in the Large Magellanic Cloud (2011, background): “…destruction close to the remnant (Reach et al., 2002); (v) the dust abundances and properties are thought to evolve with the metallicity of the ISM (Galliano et al., 2003, 2005, 2008a); (vi) a transition from amorphous to crystalline silicates is observed in protostellar objects (e.g. Hallenbeck…”
• MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES (2009, background): “Within this context, the relative strength of PAH features can be used to probe the energetics of the underlying radiation field (e.g., Galliano et al. 2008).”
• THE INFRARED SPECTRA OF VERY LARGE IRREGULAR POLYCYCLIC AROMATIC HYDROCARBONS (PAHs): OBSERVATIONAL PROBES OF ASTRONOMICAL PAH GEOMETRY, SIZE, AND CHARGE (2009, background): “…the modern universe (e.g., Cox & Kessler 1999; Helou et al. 2000; Vermeij et al. 2002; Peeters et al. 2004; Bregman & Temi 2005; Brandl et al. 2006; Sellgren et al. 2007; Smith et al. 2007; Galliano et al. 2008) and detailed PAH models have been developed (e.g., Li & Draine 2001; Draine & Li 2007).”
• THE NASA AMES POLYCYCLIC AROMATIC HYDROCARBON INFRARED SPECTROSCOPIC DATABASE: THE COMPUTED SPECTRA (2010, unknown): “…of the PAH carriers (e.g., Joblin et al. 1994; Li & Draine 2001; Hony et al. 2001; Peeters et al. 2002; van Diedenhoven et al. 2004; Mulas et al. 2006; Bauschlicher et al. 2008, 2009; Galliano et al. 2008; Boersma et al. 2009, 2010; Mattioda et al. 2009; Ricca et al. 2010, and references therein).”
• The dusty torus in the Circinus galaxy: a dense disk and the torus funnel (2013, background): “3 On scales of tens of arcseconds (>200 pc) however, the Circinus galaxy indeed shows significant PAH emission at 7.7, 8.6 and 11.3 μm (Moorwood et al. 1996; Galliano et al. 2008), most likely from the circumnuclear starburst.”
• Polycyclic aromatic hydrocarbon processing in a hot gas (2009, background): “Finally, bright PAH emission has been detected associated with the hot gas of the galactic wind driven by the starburst in the nucleus of the nearby irregular galaxy, M 82 (Engelbracht et al. 2006; Beirão et al. 2008; Galliano et al. 2008).”