SPECKLE IMAGING OF ACTIVE GALACTIC NUCLEI: NGC 1068 AND NGC 4151.

摘要

High-resolution images of NGC 1068 and NGC 4151 in the (O III) 5007A line and the nearby continuum produced from data taken with the PAPA photon-counting imaging detector using the technique of speckle imaging are presented. The images show an unresolved core of (O III) 5007A emission in the middle of an extended emission region. The extended emission tends to lie alongside the subarcsecond radio structure. In NGC 4151, the extended emission comes from a nearly linear structure extending on both sides of the unresolved core. In NGC 1068, the extended emission is also a linear structure centered on the unresolved core but the emission is concentrated in lobes lying to either side of the major axis. The continuum of NGC 4151 is spatially unresolved. The continuum of NGC 1068 is extended {dollar}sim{dollar}1" to the SW of the center of the (O III) 5007A emission. Certain aspects of the PAPA detector are discussed, including the variable-threshold discriminators that track the image intensifier pulse height and the camera artifacts. The data processing is described in detail. The modulus of the object's Fourier transform is recovered using Labeyrie's technique of speckle interferometry. The phase of the transform is recovered using the Knox-Thompson technique. The modulus and phase estimates are improved with non-linear signal processing that generates estimates consistent with physical constraints on the image. A new algorithm based on projections onto convex sets is described and is used to estimate the modulus. The Knox-Thompson phases are improved with Fienup's iteration. An estimate of the noise in the resulting images is presented.