To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
It is shown that, in the case of NGC 5548, photoionization models cannot account for line fluxes, line ratios, and line variations. The assumption that a fraction of the broad-line region is mechanically heated can solve the problem.
If accretion disks are present in AGN and extend to large radii they should contribute substantially to the Broad Line emission. The outer regions of the disk are indeed illuminated by a small amount of ionizing radiation. X-rays are emitted by the central inner region near the black hole, and they are either received directly by the outer disk, owing to its “flaring” shape (Cunningham, 1976), or partly reflected towards the disk by a hot Compton thin medium (Begelmann and McKee, 1983). X-ray photons are also produced through the Inverse Compton mechanism in compact radio sources located above the disk(“jet model”).
Our knowledge of the physical conditions and of the structure of the broad line emissive region -the BLR- is reviewed. First we derive the model independent constraints on the different zones emitting the broad lines. Then we discuss photoionized models. In a first step the BLR is assumed to be made only of one type of cloud emitting all the broad lines. We show that this model is unable to explain the observed spectrum. We thus assume that the high and low ionization lines are emitted by different clouds, still photoionized. This assumption is also in contradiction with the observations and we are led to the idea of a large variety of emitting clouds. Finally the hypothesis of a purely radiative heating mechanism should also be questioned.
Many people have attacked the problem of synthesizing the stellar population of the galaxies. We have performed such a synthesis, by using only the intensities of absorption lines in the nuclei of galaxies. It is then possible to obtain a synthesized continuous spectrum even if there are several possible solutions for the stellar composition, and the computed continuum does not vary much with the assumed model of stellar population.
The method is to fit the equivalent widths of the absorption lines using different stellar compositions. In order to avoid any instrumental effect, we have observed different lines and bands from 3500 to 8500 å in stars of various well-known stellar types and luminosity classes, under the same conditions as the galaxies.
We have applied this method to some ‘ordinary’ nuclei and to some Seyfert ones. As an example, we show the results for M81 and for NGC 1068.
Email your librarian or administrator to recommend adding this to your organisation's collection.