Emission-Line Variability of Fairall 9: Determination of the Size of the Broad-Line Region and the Direction of Gas Motion

Abstract

A cross-correlation analysis has been performed on 118 IUE spectra of Fairall 9 available from 1978 to January 1987 to determine the size of the broad-line region and the average direction of gas motion. Analysis of the line flux shows that the C IV λ1549 emitting region is 124 +/- 39 light days from the central source and the Mg II λ2800 emitting region is 167 +/- 61 light days from the central source. Analysis of the wing flux indicates, that for the C IV emitting gas, pure outflow is excluded at the 98% confidence level, and there is only a 10% probability of the observed cross-correlation peak being produced by totally chaotic or circular motion. The dominant motion is therefore inward. The Mg II emitting gas suggests totally random or chaotic motions. Both pure inflow and pure outflow of this gas can be excluded at the 98% confidence level. The significance levels have been calculated theoretically and also by Monte Carlo simulations. The probability of failure of the cross-correlation technique is less than 3% in each case. The above results indicate that the gas motion in the broad-line region is dominated by gravity close to the central supermassive object, and this permits a simple kinematic determination of the mass of the black-hole. If the gas is assumed to be inflowing (the most likely case), and a characteristic velocity is assigned to the broad-line material, then the mass of the black hole is 7.7 +/- 4.9 x 10^8^ M_sun_.