Thesis Topic: Planetary Nebulae and HII regions in the Elliptical Galaxy NGC 5128

 

Thesis Supervisors: Marina Rejkuba, Jeremy R. Walsh

 

 


Abstract

NGC 5128 is the closest example of a giant early type (elliptical or S0) galaxy. Although often dubbed as a peculiar elliptical galaxy since it has a dust lane with recent star formation and an active galactic nucleus, the majority of early type galaxies have similar structures as revealed by recent surveys. At a distance of 3.8 Mpc, spectra of hundreds of the brighter planetary nebulae (PNe) are within reach of large telescopes and photometry of individual stars can be made with the cameras aboard HST and VLT. Together, these observations open up the star formation history of NGC 5128 to quantitative investigation.

The spectrum of a planetary nebula, the shell of gas ejected from an evolved low mass (<8 Msun) star and ionized as the star heats up, presents a unique opportunity to determine abundances of the lighter elements (e.g. He, N, O, Ne, S and Ar). The spectroscopic determination of abundances for these stellar ejecta can be complemented by photometrically derived abundances (by fitting to stellar evolution models) and by integrated light spectroscopy of the bulk of the stars. Planetary nebulae are not just probes of the stellar abundances - they can be easily detected from their strong emission lines and their radial velocities measured. The radial velocities are a sensitive tracer of the galaxy kinematics and kinematic sub-structures among the PNe may provide direct evidence of recent mergers.

This project can use a number of data sets already collected on NGC 5128. The topics covered are: analysis and extension of a large area imaging survey undertaken with EMMI camera on NTT 3.5m telescope in La silla aiming to detect a very large sample of new PNe in NGC 5128; kinematic modelling applied to a radial velocity survey of PNe including more than 1000 objects observed with the multi-fibre instrument FLAMES on the VLT; reduction and analysis of spectra of a sample of PNe in the area of a kinematic sub-structure (suspected merger galaxy remnant) obtained with the FORS2 instrument on the VLT; reduction and analysis of VLT FORS2 spectroscopy of the HII regions associated with young stars in the dust lane in order to relate the gas metallicity to that of the old stars and the PNe. A Ph.D. topic within these rich datasets and extension with further observations is invited.

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