Components of the ISM
•Gas (hydrogen and helium)
–Clouds
•Molecular Clouds T~20K, n>1000/cc
•Cold HI (neutral H) T~100K, n~20/cc
•Warm HI T~5000K, n~0.1-1/cc
–Diffuse gas
•HII regions (ionized H) T~10000K, n~0.01-0.1/cc
•Hot intercloud medium T~1 million K, n~0.001/cc
(most of
the volume)
•Dust (silicates, graphites, ices)
–Dark Clouds
–Cirrus
