Two-phase models of quasar emission line regions

Journal Article · Thu Oct 15 04:00:00 EDT 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/159303· OSTI ID:5426708

Krolik, J H; McKee, C F; Tarter, C B

Previous studies of quasaremission line regions have established that the emitting gas as in clouds occupying a small fraction of the available volume and have suggested that these clouds are confined by ahot intercloud medium. We demonstrate that the clouds must be confined, provided only that the heating mechanisms are strong enough to drive the temperature of the low density intercloud gas above a few 10/sup 7/ K. We have analyzed the thermal properties of the cloud-intercloud system under the assumption that it is in thermal balance (heating equals cooling), although wedo not rule out the possibility that the intercloud gas is so hot (possibly relativistic) that it isfarfrom equilibrium. If it is in thermal balance, then the cloud-intercloud system is in a two-phase equilibrium only for a relatively narrow range of the radiation-to-gas pressureratio, including the range actually observed for the emission line clouds. Our study of the thermal properties of the gas includes heating by photoionization, Compton scattering, supeathermal particles, absorption of radiofrequency radiation, cloud friction, thermal conduction, and shocks; under steady-state conditions as considered here, this heating is balanced by collisional and Comptom cooling, and, for very hot intercloud gas, ionization losses in the clouds.Cooling curves for photoionized gases are presented. Phase diagrams analogous to the pressure-temperature diagrams used in studying the interstellar medium are constructed for a variety of conditions. Two-phase equilibria occur over a wide range of mean density but over a considerably narrower rangeof pressure. Most of the mass in the emission line region is in the hot intercloud medium, but its X-ray luminosity is generally too small to allow detection. The implications of these results for the emission line region are briefly discussed; in particular we show that the emission clouds may be short-lived, in contrast to the conventional picture.

• Research Organization: Center for Space Research, Center for Theoretical Physics, and Physics Department, Massachusetts Institute of Technology
• OSTI ID: 5426708
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 249:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
640105 -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION
BASIC INTERACTIONS
COMPTON EFFECT
COOLING
COSMIC GASES
COSMIC RADIO SOURCES
DIAGRAMS
ELASTIC SCATTERING
ELECTROMAGNETIC INTERACTIONS
ELECTROMAGNETIC RADIATION
EMISSION SPECTRA
EQUILIBRIUM
FLUIDS
GASES
HEATING
INTERACTIONS
IONIZATION
PHASE DIAGRAMS
PHASE STUDIES
PHOTOIONIZATION
PHYSICAL PROPERTIES
QUASARS
RADIATIONS
RADIOWAVE RADIATION
SCATTERING
SPECTRA
STEADY-STATE CONDITIONS
THERMAL CONDUCTIVITY
THERMAL EQUILIBRIUM
THERMODYNAMIC PROPERTIES