6.1. Observing strategies
Recent results suggest the following observational strategies might be
- Observe two bandpasses (e.g. V and I) so that
possible systematic effects with
color (metallicity and age) can be identified and removed (see
Ashman, Conti, & Zepf 1995,
and Elson & Santiago 1996b).
- Observe farther toward the infrared (e.g. I band) to
minimize possible correlations
of M0V with metallicity (see
Ashman, Conti, & Zepf 1995).
- For HST observations, use dithered exposures to help remove hot
pixels and improve spatial resolution.
6.2. Future Work
What are the key observations likely to be over the next five years?
- The determination of whether the GCLF is different for
spiral and elliptical galaxies.
The most straightforward approach would be to use HST to observe spirals and
ellipticals in tight groups, or possibly in pairs.
- A better determination of the zeropoint for the GCLF in bright
elliptical galaxies using Cepheid variables in the Virgo, Fornax, and
other nearby groups and clusters. This
will remove the dependence on spiral galaxies where the GCLF is less
- A better determination of the appropriate expansion velocity to
use for the estimate of the Hubble constant. While the
Jerjen & Tammann (1993)
approach is promising, it can be improved using the more extensive data
currently available. In addition, the
same method should be used for the Fornax cluster and other key groups
where Cepheid measurements are available (e.g. the Leo group).
- Observations of the GCLF in a sample of bright elliptical galaxies
with good sky coverage in the range 2,000 - 10,000 km s-1
(with HST) to minimize the dependence on peculiar velocities.
- The GCLF for bright ellipticals turns out to be an
excellent distance indicator,
much better than might be expected based on current theoretical ideas
about the formation and destruction of clusters. The intrinsic
dispersion in M0V is
- The value of M0V appears to be nearly
universal. The current database can begin
to support the search for possible (small) second-order correlations of
M0V with various
properties (e.g. Hubble type, color, environment).
- Cepheid variables can be used to determine the GCLF zeropoint for
rather than relying on the Milky Way, M31, and an assumption of universality.
- HST provides an excellent tool for measuring the GCLF, providing
limiting magnitudes roughly two to three magnitudes deeper than
- The number of high quality GCLFs will increase dramatically in the
making this one of the most important methods of measuring distances.