Photoelectric heating of interstellar gas
B. T. Draine;
ApJS, 1978, 36, 595
ABSTRACT:Photoelectric emission from interstellar grains and its consequences for the heating and cooling of interstellar gas are reexamined.
The
physics of photoemission is briefly reviewed, the photoemissive properties
of interstellar grains are examined, and the absorption efficiency and
total geometric cross section of the grains are estimated.
Some aspects of
gas-grain interactions are considered, the interstellar UV energy density is
discussed, and the grain potential and heating rate are evaluated for the
interstellar UV background as well as for a wide range of electron densities and
temperatures.
Steady-state solutions for the gas are obtained, and their relevance to the
interstellar medium is briefly assessed.
The time-dependent cooling of a fossil H
II region is analyzed, and it is suggested that fossil H II in the wakes of
runaway O stars can produce significant amounts of intermediate-temperature
(about 500 to 3000 K) H I.
It is concluded that: (1) interstellar grains are
likely to have effective photoelectric thresholds of approximately 8 eV and
(2) photoemission from grains is a major contributor to the heating of the
cool phase of the interstellar medium.
KEYWORDS: gas heating, interstellar gas, photoelectric emission, radiant cooling, cations, gas ionization, gas temperature, h ii regions, scaling laws, spiral galaxies, steady state, time dependence, ultraviolet radiation
PERSOKEY:general ism, dust, ,
CODE: draine78