Modelling the Spoon IRS diagnostic diagram |
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| Authors: | Michael Rowan-Robinson Andreas Efstathiou |
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| Institution: | Astrophysics Group, Blackett Laboratory, Imperial College of Science Technology and Medicine, Prince Consort Road, London SW7 2AZ;School of Sciences, European University Cyprus, Diogenes St, Engomi, 1516 Nicosia, Cyprus |
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| Abstract: | We explore whether our models for starbursts, quiescent star-forming galaxies and for active galactic nuclei (AGN) dust tori are able to model the full range of Spitzer Infrared Spectrograph (IRS) spectra measured with Spitzer . The diagnostic plot of 9.7 μm silicate optical depth versus 6.2 μm polycyclic aromatic hydrocarbon (PAH) equivalent width, introduced by Spoon and coworkers in 2007, gives a good indication of the age and optical depth of a starburst, and of the contribution of an AGN dust torus. However, there is aliasing between age and optical depth at later times in the evolution of a starburst, and between age and the presence of an AGN dust torus. Modelling the full IRS spectra and using broad-band 25–850 μm fluxes can help to resolve these aliases. The observed spectral energy distributions require starbursts of a range of ages with initial dust optical depth ranging from 50–200, optically thin dust emission ('cirrus') illuminated by a range of surface brightnesses of the interstellar radiation field, and AGN dust tori with a range of viewing angles. |
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| Keywords: | star: formation galaxies: evolution infrared: galaxies galaxies: starburst cosmology: observations |
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