Radiative cooling and viscous dissipation in molecular accretion disks at the nuclei of galaxies

Steven Desch, B. K. Wallin, W. D. Watson

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Key processes are examined in the heating and cooling of molecular gas with emphasis on environments for water masers at the nuclei of galaxies. The exchange of infrared radiation between the gas and dust grains is evaluated in determining the cooling of the gas and in determining the thermal coupling between the gas and the dust grains. Calculations are performed for the transport of continuum radiation through an optically thick slab to assess the temperatures of the dust grains. The highly refined observational description of the subparsec circumnuclear disk in the galaxy NGC 4258 serves as a focus. The viscous dissipation that is inherent in an accretion disk is reconsidered as a source of heat to create the masing environment. Based on our cooling rates, the input of energy that is required to create the bulk of the observed masing gas is evaluated and is found to be comparable in magnitude (per unit surface area) to that generated by the viscous dissipation. To be effective in actually creating the masing environment, the distribution for the viscous dissipation of heat with distance from the midplane of the disk must be quite different from the distribution of the mass. Tentative evidence that this is plausible is discussed. One consequence is the likely presence of a component of the disk at the midplane that is colder and much more massive than the masing gas. The recent interpretation that the inner disk of NGC 4258 may be advective is especially useful for this description, since the viscous dissipation at the location of the masers tends to be enhanced. A significant temperature difference between the gas and the grains, which is necessary for masing, is found to result regardless of whether the heating in these environments is provided by viscous dissipation or by X-rays.

Original languageEnglish (US)
Pages (from-to)775-785
Number of pages11
JournalAstrophysical Journal
Volume496
Issue number2 PART I
DOIs
StatePublished - 1998
Externally publishedYes

Fingerprint

accretion disks
dissipation
accretion
galaxies
cooling
nuclei
gases
gas
dust
water masers
heat
heating
infrared radiation
molecular gases
masers
temperature gradients
slabs
slab
continuums
surface area

Keywords

  • Accretion, accretion disks
  • Dust, extinction
  • Galaxies: Nuclei
  • Masers
  • Molecular processes
  • Radiative transfer

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Radiative cooling and viscous dissipation in molecular accretion disks at the nuclei of galaxies. / Desch, Steven; Wallin, B. K.; Watson, W. D.

In: Astrophysical Journal, Vol. 496, No. 2 PART I, 1998, p. 775-785.

Research output: Contribution to journalArticle

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