main difference between either method and the unextinguished case represented on the top panel of Figure \[figN\] is the absence of the inner layer of ionized gas. Central temperatures and pressures are almost two orders of magnitude lower, and, since there is no phase transition associated to any ionization front, the density of the cold neutral material is equal to $n_0$, also orders of magnitude lower than in the model without attenuation.

The absorption of the ultraviolet photodissociating radiation turns out to be very important as well. The location of the transition from the cold to the warm neutral phase may change by a large factor, but the most relevant issue is the predicted fraction of Hydrogen in molecular form. In particular, the [[extinguish]{}]{} command overestimates the photodissociation rate so much that there is virtually no molecular Hydrogen at all. Our results can only strengthen the advice given in Hazy of modelling the absorbing material rather than using the [[extinguish]{}]{} command.

Stellar mass and Galactic magnetic field
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![ Total stellar mass density (solid line) and contributions of individual populations with different ages (dotted lines) according to @Robin+03. The approximation given in equation (\[eqRhoStar\]) is shown as a dashed line. 