Velocity dispersion of individual NGC 5128 globular clusters and the fundamental plane for extragalactic globular clusters.
Session 52 -- Elliptical Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

## [52.03] Velocity dispersion of individual NGC 5128 globular clusters and the fundamental plane for extragalactic globular clusters.

P. Dubath (UCO/Lick Observatory)

Galactic globular clusters show tight correlations between velocity dispersion, luminosity and a physical scale, as expected from the Virial Theorem or the King models. These correlations are analogous to the fundamental plane correlations for elliptical galaxies. New data for old LMC globular clusters show a possibly significant deviation. One of the most basic of these correlations is the tight relation between the absolute magnitude and the logarithm of the velocity dispersion. The first velocity dispersion determinations for 8 of the brightest globular clusters belonging to the peculiar elliptical galaxy NGC 5128 (Centaurus A) are presented, based on high-resolution NTT spectroscopic data. These clusters are 0.5-1 magnitude intrinsically brighter than $\omega$\thinspace Cen, the most luminous (giant) Galactic globular cluster. Their global velocity dispersions range from 15 to 25 km\thinspace s$^{-1}$. These values fall almost perfectly on the extrapolation of the best Galactic cluster relation $\sigma$ $\sim$ L$^{1/2}$. The validity of this relation is, therefore, extended to brighter globular clusters. This indicates similarities, in terms of structure and mass-to-light ratio, between the NGC 5128 and the Galactic globular clusters.

Using the Galactic relation to estimate the absolute magnitude from the velocity dispersion, a distance modulus can be derived for each NGC 5128 globular cluster. Their average provide a NGC 5128 distance modulus consistent with the recent determinations from planetary nebula luminosity function or surface brightness fluctuation.