THE BROAD LINE REGION IN NGC 4051: AN INFLOW ILLUMINATED BY A 105 K ACCRETION DISK

Adopting a spherically symmetric steady-state ballistic inflow as the kinematic model for the gas distribution responsible for producing the H{alpha} emission line, and a central black hole (BH) mass of 1.7 Multiplication-Sign 10{sup 6} M{sub Sun} determined from prior reverberation mapping, leads to the following dimensions for the size of the broad line region (BLR) in NGC 4051; an inner radius {approx}3 lt-day and a lower limit to the outer radius {approx}475 lt-day. Thus, the previously determined reverberation size for the BLR marks just the inner radius of a much larger volume of ionized gas. The number of ionizing photons required to sustain the H{alpha} emission line luminosity exceeds the number observed to be available from the central active galactic nucleus (AGN) by a factor of 3-4. Such a large ionizing deficit can be reconciled if the BLR is ionized by a 10{sup 5} K accretion disk that is hidden from direct view by the high opacity of intervening H gas. A new definition is introduced for the ionization parameter that acknowledges the fact that H opacity significantly attenuates the flux of ionizing photons in the large, partially ionized nebula surrounding the AGN. Collectively, the results have important implications formore » BH masses estimated using reverberation radii and the structure of the BLR inferred from velocity-delay maps.« less