IAU Circulars 7065 and 7155 . With Robin Ciardullo and John Feldmeier , Jacoby has been exploring the population of stars between galaxies in the Fornax and Virgo clusters of galaxies. We have been using the WIYN observatory and the ESO VLT to obtain velocities of the PN between the galaxies in Virgo. The observation and analysis of planetary nebula motions in galaxies is of growing interest because there is no better way to measure the stellar velocities, especially for these very faint stars in Virgo. The velocities will map out the distribution and quantity of dark matter in the Virgo cluster far better than the galaxies because there are hundreds of thousands of PN and only a few hundred galaxies.
Preliminary results show that the bulge of the galaxy is rotationally supported.
Also, there are about 10 times fewer stars in the galaxy halo that produce planetary nebulae than initially thought, possibly evidence for either a very low mass or a very old halo. Nevertheless, there seem to be several times more halo PN in M31 than in our own Galaxy. In most of the remaining cases, it will not be possible to make the measurements because the nebulae are extremely faint, being extinguished by an enormous of dust between the Galactic center and the Earth. Thus, each nebula that can be studied is an important one. We are continuing our analysis of the existing spectra.