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7. Structure and dynamic of the BLR

With the results obtained above from the behavior of the broad-line components we will try to derive the structure of the BLR in some detail, under the assumption that the gas producing these components is gravitationally bound. Then the mass of the central object (the black hole in the standard theory) can be calculated, as usual, from tex2html_wrap_inline7925, where v is the gas velocity and r its distance to the object. We find the distance can be estimated from the delays obtained with the correlation functions in combination with the distances deduced from the central photoionization models. To determine the velocity we assume that the main mechanism of line-broadening is macroscopic turbulent movement, implying that the mean velocity is tex2html_wrap_inline7931. For the central component this gives tex2html_wrap_inline7933 tex2html_wrap_inline7935. Its distance to the central object is more difficult to establish, due to the fact that the one deduced from the CCF, tex2html_wrap_inline7939, is twice as large as that from the photoionization models of tex2html_wrap_inline7941. This could indicate some special geometry with respect to the observer, which will be discussed below. For the current discussion we will use a distance of tex2html_wrap_inline7943, obtaining tex2html_wrap_inline7945, equal to the estimated one by Clavel et al. (1989). The similarity in these results is not too surprising since we find a smaller distance but the turbulent velocity of the individual component is compensating for this.

If we now use this value of M and the FWHM for the blue and the red components, distances of 75 and 77 light-days, respectively, are obtained. This tex2html_wrap_inline7951 distance, equal for both components, is significantly different from the delay calculated from the correlation functions, tex2html_wrap_inline7953 and tex2html_wrap_inline7955, respectively. This can be explained if infalling motion of the gas at a distance of tex2html_wrap_inline7957 is considered, because then the red flux does not lag behind the continuum variations and the blue flux will be delayed by twice the light travel time (Koratkar & Gaskell 1991). Koratkar & Gaskell, applying cross correlations to the wings of the Fairall-9 lines, obtain for CIV tex2html_wrap_inline7959 and tex2html_wrap_inline7961 for the red and the blue flux, respectively, concluding that the gas producing these fluxes is at a distance of tex2html_wrap_inline7963 and has an infall movement, compatible with our result. However, they obtain for tex2html_wrap_inline7965 that both wings are delayed with respect to the continuum tex2html_wrap_inline7967, suggesting that the movement is chaotic or circular. We have not been able to analyze the wings of tex2html_wrap_inline7969 because the correlation functions are not significant due to the small variability amplitude of the tex2html_wrap_inline7971 flux with the continuum.

Supposing that the red and the blue components of Lytex2html_wrap_inline7973, CIV and SiIV are produced in the same zone of gas at tex2html_wrap_inline7975 and is infalling, there is a problem if this region is spherically symmetric. In that case we should obtain central gas at the same distance, while we find that the central component originates further away. The absence of this central gas indicates a non-spherically symmetric or anisotropic continuum emission, so that the majority of the gas responsible for the red and the blue flux is along the line of sight of the observer (the angular extend of course limited by the time resolution of our data). Besides, the central component is produced at a larger distance, tex2html_wrap_inline7977, explaining the derived twice larger delay if this region of gas is behind the source, suggesting that either the symmetry is non-spherical or the continuum emission is anisotropic, or both. The absence of central gas between the source and the observer could, in this context, be explained as due to the presence of dust in the non-illuminated or neutral part of the clouds, which would absorb its emission. Then the dust emitting in the near IR at tex2html_wrap_inline7979 (Clavel et al.\ 1989) should extend between tex2html_wrap_inline7981 and larger distances.


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