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Astron. Astrophys. 337, 85-95 (1998)

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5. Conclusion

We described an efficient and numerically stable algorithm, based on the results of Guhathakurta & Draine (1989) and Léger et al. (1989), to calculate the quantum heating of small dust grains and of PAHs. The iterative procedure, combined with adaptive temperature grids and quality checks (conservation of energy, spectral deviation) leads to reliable results for all kinds of grain sizes and radiation fields. We demonstrated the need for such algorithms to calculate quantum heating at a reliable accuracy, especially if quantum heating should be used in radiative transfer calculations, in the presence of grain size distributions, and for various types of local radiation fields.

For the first time, a quantum heating algorithm is included in a 2D radiative transfer code. This new code enabled us to model the IR emission of the starburst galaxy NGC 6090. Our calculations proved that quantum heated small particles influence significantly the SED as well as the intensity maps of the dust torus. It even happens that continuum emission of small grains is the dominant source of dust radiation at most NIR to MIR wavelengths, for all points inside the dust torus. Naturally, this effect is much stronger for the emission lines of the PAHs.

Despite the fact that it may be possible to fit the continuum emission using dust composed only of big grains, the results obtained this way would lead to a completely wrong interpretation of the observations, because completely different density and temperature distributions would be derived. Therefore, we conclude that any modeling concerning dusty objects which show PAH lines must include quantum heating if reliable interpretations of the data are the goal.

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© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998