Optically thin thermal emission from cold clouds in active galactic nuclei

Details Optically thin thermal emission from cold clouds in active galactic nuclei Optically thin thermal emission from cold clouds in active galactic nuclei

Jul 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...335..881t&link_type=abstract

Astronomy and Astrophysics, v.335, p.881-893 (1998)

Astronomy and Astrophysics

Astrophysics

7

Radiation Mechanisms: Thermal, Ultraviolet: Galaxies, Galaxies: Nuclei, Galaxies: Seyfert, Galaxies: Quasars: General

Scientific paper

The thin thermal emission from an ensemble of cold condensations embedded in a hot plasma is investigated. The temperature distribution inside the cloud is derived by integrating the energy equation where heating, radiative losses and thermal conduction balance each other. The presence of the thermal conduction term, which constitutes the main difference with respect to the previous models, determines the scale length of the cloud and makes the cold cloud core very narrow while the surrounding shell, only slightly cooler than the external medium, is very extended. It follows that the emission from the cold core is negligible with respect to that of the extended shell, which in turn can be more luminous than the surrounding medium only if a strong negative pressure gradient is introduced. Hence, the emission from such a configuration does not show a thermal peak characterized by a temperature value ranging from 10(5) to 10(6) K as observed in the active galactic nuclei (AGN) spectra. These conclusions are independent of the selected heating and loss functions and also the introduction of a magnetic field cannot change them. If evolving structures can be a viable solution to this problem is also briefly analyzed.

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