Extragalactic Planetary Nebulae

The central stars of planetary nebulae are among the brightest objects in a galaxy. However, these objects are so hot that most of their light comes out, not in the visible, but in the far ultraviolet end of the spectrum. The EUV light gets absorbed by the surrounding gas and re-emitted in a series of emission lines, the brightest of which is a line of doubly-ionzed oxygen. In fact, almost 15% of the continuum energy of central star is reprocessed into emission at a single wavelength of green light at 5007 Angstroms.

The [O III] planetary nebula luminosity function is one of the most accurate tools for determining the Extragalactic Distance Scale and Hubble Constant

The number of bright planetary nebulae in an elliptical galaxy is a sensitive probe of the galaxy's underlying stellar population.

Radial velocity measurements of the hundreds of PN present in an elliptical galaxy's halo are an ideal way to learn about elliptical galaxy stellar kinematics and dark matter content .

PN line ratio measurements provide information about the chemistry of the interstellar medium at the time of the progenitor's formation and the history of galactic chemical evolution .

The distribution and kinematics of intergalactic PN in clusters provide strong constraints on the structure of galaxy clusters, their matter distribution, and dynamical history.