Interstellar Medium - Interstellar Matter

Interstellar Matter

Table 1 shows a breakdown of the properties of the components of the ISM of the Milky Way.

Table 1: Components of the interstellar medium
Component Fractional
Volume		 Scale Height
(pc)		 Temperature
(K)		 Density
(atoms/cm³)		 State of hydrogen Primary observational techniques
Molecular clouds < 1% 80 10—20 102—106 molecular Radio and infrared molecular emission and absorption lines
Cold Neutral Medium (CNM) 1—5% 100—300 50—100 20—50 neutral atomic H I 21 cm line absorption
Warm Neutral Medium (WNM) 10—20% 300—400 6000—10000 0.2—0.5 neutral atomic H I 21 cm line emission
Warm Ionized Medium (WIM) 20—50% 1000 8000 0.2—0.5 ionized Hα emission and pulsar dispersion
H II regions < 1% 70 8000 102—104 ionized Hα emission and pulsar dispersion
Coronal gas
Hot Ionized Medium (HIM)		 30—70% 1000—3000 106—107 10−4—10−2 ionized
(metals also highly ionized)		 X-ray emission; absorption lines of highly ionized metals, primarily in the ultraviolet

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