Minimum heating intensity derived from the SED model using submm data compared to minimum heating intensity determined without submm data. The orange line indicates the 1:1 relation. The dashed lines define the limits Draine et al. (2007) used as boundaries for their minimum heating intensity U_min. We remind the reader that our model solutions are obtained with U_min as a free parameter. For convention on symbols, see Fig. 4. Limiting U_min to 0.7 avoids an overestimate of the dust mass but removes the possibility of low temperature radiation fields.