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arXiv · astro-ph/0609024

The Mid-IR Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy

B. R. Brandl·J. Bernard-Salas·H. W. W. Spoon·D. Devost·G. C. Sloan·S. Guilles·Y. Wu·J. R. Houck·L. Armus·D. W. Weedman·V. Charmandaris·P. N. Appleton·B. T. Soifer·L. Hao·J. A. Marshall·S. J. Higdon·T. L. Herter
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Abstract

We present 5-38um mid-infrared spectra at a spectral resolution of R~65-130 of a large sample of 22 starburst nuclei taken with the Infrared Spectrograph IRS on board the Spitzer Space Telescope. The spectra show a vast range in starburst SEDs. The silicate absorption ranges from essentially no absorption to heavily obscured systems with an optical depth of tau(9.8um)~5. The spectral slopes can be used to discriminate between starburst and AGN powered sources. The monochromatic continuum fluxes at 15um and 30um enable a remarkably accurate estimate of the total infrared luminosity of the starburst. We find that the PAH equivalent width is independent of the total starburst luminosity L_IR as both continuum and PAH feature scale proportionally. However, the luminosity of the 6.2um feature scales with L_IR and can be used to approximate the total infrared luminosity of the starburst. Although our starburst sample covers about a factor of ten difference in the [NeIII]/[NeII] ratio, we found no systematic correlation between the radiation field hardness and the PAH equivalent width or the 7.7um/11.3um PAH ratio. These results are based on spatially integrated diagnostics over an entire starburst region, and local variations may be ``averaged out''. It is presumably due to this effect that unresolved starburst nuclei with significantly different global properties appear spectrally as rather similar members of one class of objects.

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B. R. Brandl, J. Bernard-Salas, H. W. W. Spoon, D. Devost, G. C. Sloan, S. Guilles, Y. Wu, J. R. Houck, L. Armus, D. W. Weedman, V. Charmandaris, P. N. Appleton, B. T. Soifer, L. Hao, J. A. Marshall, S. J. Higdon, T. L. Herter. 2006-09-01. The Mid-IR Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy. https://doi.org/10.1086/508849%2010.1086%2F519993

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