The stellar and dark matter halo of NGC 5128 (Centaurus A).

摘要

In this dissertation, we address the issues of elliptical galaxy formation in a detailed investigation of the galaxy NGC 5128 (Centaurus A). Our survey consisted of multiple parts: (1) A narrowband imaging survey for planetary nebulae (PNe) with spectroscopic followup to obtain radial velocities. We now know of 1141 PNe in NGC 5128, 780 of which are confirmed. Of these 780 PNe, 349 are new front this survey, and 148 are at radii beyond 20 kpc. (2) A UBVRI broadband imaging survey for globular clusters (GCs) with spectroscopic followup. We developed an efficient algorithm for targeting GCs, producing new velocities for 138 GCs, bringing the confirmed total to 215. (3) An investigation of the color structure in the halo to search for recently accreted dwarf galaxies. We discovered a tidal stream of young, blue stars that is likely to be the remnant of an accreted dwarf irregular galaxy. The stream contains at least one proto-globular cluster.; Using these data, we studied the structure, dynamical state, and star formation history of NGC 5128. The major results of our investigation are: (1) PNe are detected at distances of 80 kpc, showing that the stellar halo extends to the limit of our data. (2) We confirm the large minor axis rotation of the PNe, and show that it extends in a disk-like feature into the halo. The rotation curve of the stars flattens at ∼100 km s −1 with V/σ between 1 and 1.5. (3) The two-dimensional velocity field shows that the zero-velocity contour has a pronounced twist. (4) The galaxy potential is triaxial in shape, tending toward prolate. (5) The color and metallicity distribution of the GCs is confirmed to be bimodal. (6) The metal-poor clusters appear to have old ages similar to the Galactic GCs, while the metal-rich clusters have intermediate ages of ∼4 Gyr. (7) The kinematics of the metal-rich GCs are similar to those of the PNe, showing both major and minor axis rotation. The metal-poor GC kinematics are also correlated with those of the PNe, but not as strongly. (8) The total dynamical mass of the galaxy within 80 kpc is ∼5 × 1011$M\odot$, with M/L_B ∼ 13. (Abstract shortened by UMI.)