The gas kinematics in the nucleus of seyfert galaxy NGC 5548

Abstract

A modeling of the response of the λ 1549 CIV emission line profile in the spectrum of Seyfert galaxy NGC 5548 to a sharp continuum drop which happened in 1989 is carried out on the basis of observational data taken from the literature. A more rapid response of the red wing of CIV profile suggesting the accretion of CIV-emitting clouds in the broad-line region (BLR) is reproduced. It is shown that the accretion velocity near the central object is consistent with a free fall law whereas at large distances from the center it varies approximately asr ⁻². The best agreement between observed CIV profile changes and modeled ones is obtained when the mass of the central objectM ≃ 1.2 × 10⁸ M _⊙. The first approximation of the BLR geometry is also found: the inflow takes place only outside two wide cones with half-opening angle ≃ 65° which are disposed like a sand-glass and filled by outflowing material. The angle between the axis of such biconical structure and our line of sight is found to be small (≃ 9°). It is shown that the outer radius of an accretion disk around the central object does not exceed ~ I light-day (i.e., < 100 Schwarzschild radii), and the outer radius of “CIV-emitting” BLR is ≃ 14 light-days. The nature of a broad blue excess in the CIV profile which did not respond to the continuum change is discussed.