Is the intercloud medium pervasive
C. Heiles;
ApJ, 1980, 235, 833
ABSTRACT:The pervasiveness of the 'not strongly absorbing' (NSA) H I gas, which is the intercloud medium in steady state theories of the interstellar
medium, is considered.
Wide emission components in nearby gas, and the
absence of absorption components in distant gas, are analyzed.
It is
concluded that the NSA material is deficient in the immediately local solar
vicinity.
In nearby regions it contains 38% of the interstellar H I; it is generally
pervasive and often has internal motions which greatly increase its velocity
dispersion above the 5 km/s minimum value.
It contains large holes, perhaps
ranging up to 400 pc diameter, which probably occupy 10-20% of the volume.
In
distant regions the NSA material seems to be pervasive outside 8 kpc galactic
radius, and for galactic radii between 8 and 10 kpc its thickness agrees with
previous determinations of 370 pc for nearby regions.
Outside 10 kpc the
thickness increases dramatically; inside 8 kpc there are no data.
KEYWORDS: absorption spectra, hydrogen clouds, interstellar gas, milky way galaxy, centimeter waves, emission spectra, line spectra, normal density functions, radio sources (astronomy), spatial distribution, ubv spectra
CODE: heiles80