A SURFACE PHOTOMETRIC STUDY OF NGC 5128
PENNINGTON, ROBERT LEE
Doctor of Philosophy
Calibrated digital surface photometry in the standard UBV pass- bands has been used to prepare two dimensional maps to examine the structure and stellar populations in NGC 5128 (Cen A). The main body of the galaxy exhibits colors and stellar populations slightly bluer than those of an old elliptical galaxy out to r (TURN) 176". Beyond this radius, excess emission in the inner halo contributes significantly to the U passband only, probably due to line emission from material swept into the halo from the dust lane. A gradient in B-V of (TURN)0('m)01/ 1.5 (D/3) kpc is evident along the major axis in both hemispheres. Four large diffuse arcs have been detected on the B-V raster. The outermost two are in the northern hemisphere and have similar B-V colors of (TURN)-0.11. The innermost pair are on opposite sides of the nucleus at r (TURN) 107" with B-V = 0.08, suggesting that a ring or sphere may exist at this radius, centered on the nucleus. The dust lane is found to be a hollow cylinder of inner and outer radii 2.2 (D/3) kpc and 2.6 (D/3) kpc, respectively, tilted at 80(DEGREES) (+OR-)2 to the plane of the sky. The most intense star formation regions lie on the northern rim on the near side of the lane and the southern rim on the far side. The circular shape of the lane constrains the main body of the galaxy to being prolate or only very mildly elliptical. There is evidence that the lane is being fed from the intergalactic medium along the SE edge at a rate of (TURN)1 M(,o)/year. A minimum mass for the lane is calculated to be 10('8) M(,o) based on the observed extinction in the lane to the SE of the nucleus. The presence of the inner optical jet has been confirmed and shown to coincide with features in the x-ray jet. A parallel dust ridge is present on either side of the jet, extending at least the full length of the jet. No counterjet has been detected in the southern hemi- sphere. Excess optical emission from the edges of the radio bridge connecting the nucleus and the lobes has probably been detected.