Table 3
Parameters of the model.
| Parameter | Units & normalization | Range of values | Definition | Comments |
|
|
||||
| 1. Free parameters | ||||
| M dust | [M⊙] | [0,∞ [ | Dust mass (all components; Eq. (5)) | Linearly correlated with ⟨ U ⟩ |
| f PAH | [4.6%] | [0,1/0.046] | PAH-to-dust mass ratio | Degenerate with the arbitrarily fixed |
| (relative to Galactic) | PAH charge fraction | |||
| α | ... | [1,2.5] | Index of the power-law distribution of | Correlated with Umin and ΔU |
| starlight intensities (Eq. (4)) | ||||
| U min | [2.2 × 10-5 W m-2] | [10-2,107] | Lower cut-off of the power-law distribution | Correlated with α and ΔU |
| of starlight intensities (Eq. (4)) | ||||
| ΔU | [2.2 × 10-5 W m-2] | [1,107 − Umin] | Range of starlight intensities (Eq. (4)) | Correlated with α and Umin |
| M ⋆ | [M⊙] | [0,∞ [ | Mass of the old stellar population | Poorly constrained; this parameter is |
| used only to subtract the stellar continuum | ||||
| to the mid-IR bands; this component has no | ||||
| relation to the starlight intensity | ||||
|
|
||||
| 2. Derived parameters | ||||
| L IR | [L⊙] | [0,∞ [ | Infrared luminosity (total dust power Eq. (13)) | Almost model independent |
| ⟨ U ⟩ | [2.2 × 10-5 W m-2] | [10-2,107] | Mass averaged starlight intensity (Eq. (11)) | ... |
| σ(U) | [2.2 × 10-5 W m-2] | [1,107 − ⟨ U ⟩] | Second moment of the starlight intensity | ... |
| distribution (Eq. (12)) | ||||
| G dust | ... | [0,∞ [ | Gas-to-dust mass ratio (Eq. (14)) | The Galactic value is  |
| (Zubko et al. 2004) | ||||
Notes. The first category lists the independent free parameters. The second category lists the quantities derived from these parameters. The last column (“comments”) describes the behaviour of the parameters when fitting an SED. In absolute, Mdust and ⟨ U ⟩ are independent. However, when fitting an observed SED, a slight variation of ⟨ U ⟩ will have systematic consequences on Mdust, to compensate the variation and minimize the χ2. The same comment applies to the other dependent parameters.
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