Heating of dust in the broad-line regions of active galaxies and quasars

Journal Article · Wed Dec 01 04:00:00 EST 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160478· OSTI ID:5577306

Rudy, R J; Puetter, R C

In this paper we discuss the relevant energy sources which heat (and, in many cases, destroy) the dust grains in the emission-line clouds (ELCs) which give rise to the broad-line emission seen in active extragalactic objects. We compare the heating rates from the external radiation field, trapped line radiation, and the diffuse bound-free continua. We find that in hot clouds (T/sub e/ = 1.5 x 10/sup 4/ K) Ly..cap alpha.. dominates the dust heating rate, while in cooler clouds (T/sub e/ = 1.0 x 10/sup 4/ K) the external radiation field dominates. In all cases, the dust residing in the broad-line clouds is quite hot (T>500 K). These results are discussed in light of the observed infrared properties of active galaxies and quasars, and the following conclusions are reached: (1) If the infrared emission of Seyfert 1 galaxies is primarily thermal in origin, then the redder near-IR colors distinguishing the Seyfert 1 galaxies from the Seyfert 2 galaxies may be understood in terms of the broad-line regions (BLR) concentrating hot dust within the inner parsec of the of the nucleus. (2) Substantial near-infrared dust emission may originate in the neutral regions of the ELCs with only minor accompanying reddening of the hydrogen Balmer lines, since dust confined to the neutral zone reddens only lines emitted from the back side of the cloud. (3) If the broad-line regions of the quasars are characterized by hotter temperatures than Seyfert 1 galaxies, dust may not be able to exist in this region, thereby explaining the apparent lack of thermal dust emission in quasars. (4) Because of the cooling times of the ELCs, near-IR variability due to changes in the dust temperature is dominated by light travel considerations. (5) The present calculations suggest that the dust-to-gas mass ratio in the BLRs of Seyfert 1 galaxies is substantially smaller than the value of 0.01 typically found in our Galaxy.

• Research Organization: Steward Observatory, University of Arizona
• OSTI ID: 5577306
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 263:1; 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
COSMIC DUST
COSMIC RADIO SOURCES
DUSTS
ELECTROMAGNETIC RADIATION
EMISSION
GALAXIES
GALAXY NUCLEI
HEATING
INFRARED RADIATION
INTERSTELLAR GRAINS
LYMAN LINES
NEAR INFRARED RADIATION
OPACITY
OPTICAL PROPERTIES
PARTICLES
PHYSICAL PROPERTIES
QUASARS
RADIATIONS
SEYFERT GALAXIES