Because PNe are detected as individual point sources, their
detectability is uncorrelated with surface brightness - i.e. they can
be detected no matter how faint the diffuse stellar background. This
means that the number of observed PNe can be used as a proxy for surface
brightness, no matter how faint!
Simply taking an absorption line spectrum of the ICL stellar
population is prohibitively time consuming. Emission line specta of
PNe are much easier.
- GMOS --- 8M Genimi N telescope - 55.5 hours to obatin S/N=1 for
surface brightness 28.0 mag/sq.arcsec (GMOS ITC).
- PN.S --- 4.2M WHT telescope - 19 hours (in mediocre
conditions) to obtain 214 PNe velocities
down to 29.0 mag/sq.arcsec (Douglas et al. 2007).
- Proper motion --- 500km/s velocity at 16 Mpc (Virgo distance) is
6.6x10-3 mas/yr or about 150 yr/mas
Why ICL Velocities are Useful
- Tidal streams can map the orbit of the galaxy through the cluster
potential.
- ICL features kinematically associated with galaxies can show
causal influence beyond mere projection, allowing a fuller
understanding of cluster substructure and galaxy interaction
histories.
- Relaxation state of the ICL can be used to determine the
virialization state and recent dynamical history of the cluster
potential.
- ICPNe represent ptoentially thousands of independent kinematic
tracers of the cluster potential, as opposed to tens-hundreds of
galaxies.
- Note to cosmologists who could care less about stars:
"cluster potential" = "DARK MATTER"!
- Cluster mass assembly is an important tracer of structure
formation in the universe.
- Galaxy evolution --- especially galaxy interactions --- is
essential for understanding dark matter - baryon coupling.
ICL Modeling
- Mapping the velocity field of clusters
Mean Velocity
|
Velocity Dispersion
|
- Creating "simulated observations" of ICPNe velocities in clusters
to determine:
- How many ICPNe are required?
- How deep do observations need to go?
- What areal coverage is needed?
- Results are next year's talk!
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