•So what are observed mass-to-light
ratios?
–Much
lower than critical, and now MAP seems to be confirming baryons 4% of critical,
consistent with Big Bang Nucleosynthesis (yes, we will get to this
stuff!). Dark matter helps, but only up to
about 30%.
–
•Handy numbers
–Mean galaxy luminosity is 1.25 L* =
1.55x1010 h-2 Lsun
–Typical
number density of 0.01 h-3 Mpc-3 indicates a typical galaxy separation of 5 h-1 Mpc, but of
course on those scales galaxies do cluster (Ch. 2)