Variations of the broad Hα line profile in NGC 4151 as evidence for the complex kinematics of gas in the nucleus

Abstract

A great number of spectra of the Seyfert galaxy nucleus NGC 4151 were obtained in the Crimean Astrophysical Observatory in 1988–1990 using the CCD. Significant variation in continuum intensity and broad Hα line profile were noted. Differences between individual spectra and the spectrum taken as a standard were calculated to study this variability. It was noted that different parts of the profile are varying in different ways. Smaller changes are located at far-away regions of the wings and at the low positive velocities of the profile. Lower variations in the red part of Hα profile near the center of the line are interpreted by the delay effect in an expanded shell. Since the evidences for accretion in a BIR are clisting (including NGC 4151) then either the BLR is a complex system where both inflow and low velocities outflow are observed or the outflow must be referred to the inner NLR. Cross correlation analysis shows shorter delay for the higher velocities of the Hα profile and does not contradict to the outflow at low velocities (near the line center), but its confidence level is small. Lower response to the continuum changes at far away parts of the broad Hα wings evidences that the gas in the vicinity of the central engine is optically thin for the ionizing radiation.