On the disappearance of broad-line region in low-luminosity active galactic nuclei: the role of the outflows from advection dominated accretion flows - Astrophysics > High Energy Astrophysical PhenomenaReportar como inadecuado




On the disappearance of broad-line region in low-luminosity active galactic nuclei: the role of the outflows from advection dominated accretion flows - Astrophysics > High Energy Astrophysical Phenomena - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Abstract: The broad-line region BLR disappears in many low-luminosity AGNs, thereason of which is still controversial. The BLRs in AGNs are believed to beassociated with the outflows from the accretion disks. Most of thelow-luminosity AGNs LLAGNs contain advection dominated accretion flowsADAFs, which are very hot and have a positive Bernoulli parameter. ADAFs aretherefore associated with strong outflows. We estimate the cooling of theoutflows from the ADAFs, and find that the gases in such hot outflows alwayscannot be cooled efficiently by bremsstrahlung radiation. The ADAF may co-existwith the standard disk, i.e., the inner ADAF connects to the outer thinaccretion disk at radius R tr, in the sources accreting at slightly lower thanthe critical rate. For the ADAFs with >0.001 L edd, a secondary small innercold disk is suggested to co-exist with the ADAF due to the condensationprocess. We estimate the Compton cooling of the outflow, of which the soft seedphotons either come from the outer cold disk or the secondary inner cold disk.It is found that the gas in the outflow far from the ADAF may be efficientlycooled to form BLR clouds due to the soft seed photons emitted from the colddisks, provided the transition radius of the ADAF to the outer cold disk issmall or-and the secondary small cold disk has a luminosity >0.003L edd. TheBLR clouds can still be formed in the outflows from the outer cold thin disks,if the transition radius is not very large. For the sources with <0.001L edd,the inner small cold disk is evaporated completely in the ADAF and outer thinaccretion disk may be suppressed by the ADAF, which leads to the disappearanceof the BLR. The physical implications of this scenario on the double-peakedbroad-line emitters are also discussed.



Autor: Xinwu Cao Shanghai Astronomical Observatory

Fuente: https://arxiv.org/







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