Details

Autor(en) / Beteiligte

• Smith, J. D. T
• Draine, B. T
• Dale, D. A
• Moustakas, J
• Kennicutt, Jr., R. C
• Helou, G
• Armus, L
• Roussel, H
• Sheth, K
• Bendo, G. J
• Buckalew, B. A
• Calzetti, D
• Engelbracht, C. W
• Gordon, K. D
• Hollenbach, D. J
• Li, A
• Malhotra, S
• Murphy, E. J
• Walter, F

Titel

The Mid-Infrared Spectrum of Star-forming Galaxies: Global Properties of Polycyclic Aromatic Hydrocarbon Emission

Ist Teil von

• The Astrophysical journal, 2007-02, Vol.656 (2), p.770-791

Ort / Verlag

Chicago, IL: IOP Publishing

Erscheinungsjahr

2007

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• We present a sample of low-resolution 5-38 km Spitzer IRS spectra of the inner few square kiloparsecs of 59 nearby galaxies spanning a large range of star formation properties. A robust method for decomposing mid-infrared galaxy spectra is described and used to explore the behavior of PAH emission and the prevalence of silicate dust extinction. Evidence for silicate extinction is found in6 of the sample, at strengths that indicate that most normal galaxies undergo A sub(V) 3 mag averaged over then-centers. The contribution of PAH emission to the total infrared power is found to peak near 10% and extend up to 620% and is suppressed at metallicities Z Z /4, as well as in low-luminosity AGN environments. Strong interband PAH feature strength variations (2-5 times) are observed, with the presence of a weak AGN and, to a lesser degree, increasing metallicity shifting power to the longer wavelength bands. A peculiar PAH emission spectrum with markedly diminished 5-8 km features arises among the sample solely in systems with relatively hard radiation fields harboring low-luminosity AGNs. The AGNs may modify the emitting grain distribution and provide the direct excitation source of the unusual PAH emission, which cautions against using absolute PAH strength to estimate star formation rates in systems harboring active nuclei. Alternatively, the low star formation intensity often associated with weak AGNs may affect the spectrum. The effect of variations in the mid-infrared spectrum on broadband infrared surveys is modeled and points to more than a factor of 2 uncertainty in results that assume a fixed PAH emission spectrum, for redshifts z = 0-2.5.