The Velocity Dispersion Distribution Function of Galaxies

1
The Velocity Dispersion Distribution Function of
Galaxies
Mike Pierce, Bob Berrington Sehyun Hwang (U.
Wyoming)
Background Galaxies can be broadly classified
into two groups according to their morphology
ellipticals and spirals. Spiral galaxies are
flattened by rotation into a disk-like shape
whereas ellipticals are spheroidal with no
preferred orientation for the orbits of their
stars. Furthermore, spiral galaxies are common
throughout most of space but elliptical galaxies
are found only in the densest regions, i.e.,
clusters of galaxies (Figure 1). Over the past 40
years it has become apparent that elliptical
galaxies originate through the mergers of
gas-rich spiral galaxies (Figure 2). However,
the details of this process is only now becoming
addressable through observational data. The
Project We have undertaken a large survey of the
structural properties and internal kinematics of
elliptical galaxies. The survey data consists of
imaging and spectroscopy of 2500 elliptical
within the richest, nearby clusters of galaxies.
The imaging data is currently being obtained at
WIRO and the spectroscopic data has been acquired
with the WIYN telescope on Kitt Peak. Computer
simulations are also underway in order to better
interpret the observational data. The dispersion
of stellar velocities ??? is a measure of the
mass of an elliptical galaxy. Thus ? is expected
to increase over time as a result of the merging
process. Similarly the velocity dispersion
distribution function (VDDF) for an ensemble of
ellipticals, i.e., a cluster, can be used to
measure the merging history of a given cluster.
The observed VDDF can be fit with a model (Figure
3) in order to quantify the merger history. We
are presently constructing the VDDF for all 39
clusters in our sample in order to examine the
merger history vs. other properties of these
clusters.
Figure 2
Figure 3
Figure 1