...$M_0 / (\pi R_0^2) \sqrt{G} \sqrt{9 \pi^2 / 5} / (0.53 \mu)$

The value of H_z used here is the value of the envelope whereas strictly speaking the value of H_z that one should use is the value within the disk. Since in practice, it is typically only few times larger (Fig. 2 of Paper I) and since we do not have analytical expression for the value in the disk, we use the value in the envelope.

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