Diffuse ionized gas

银河系中的DIG

• Referred to as the Reynolds layer, or warm ionized medium (WIM);
• This warm (10^4 K), diffuse (n ~ 0.2 cm~3) gas fills 20% of the disk volume and accounts for most of the mass of ionized gas.
• In terms of energetics, the Galactic WIM requires at least 10^42 ergs s~1 to remain ionized. This power is more than can be comfortably supplied by supernova shocks, but significantly less than the Lyman continuum luminosity of massive stars.