Wilford describes the work of Tod Lauer and Marc Postman, who made
a large survey of brightest-galaxies-in-clusters all over the sky.
For a sample of galaxies with velocities of up to 15,000 km/sec, they

           1. measured the redshift of the galaxy
           2. performed careful photometry of the galaxy

  The idea of their survey is to detect 'peculiar velocities', which
are simply the residuals left over after one subtracts the smooth
Hubble flow from a galaxy.  An example: suppose you see a galaxy at
a distance of 10 Mpc, and you believe the Hubble constant is
100 km/s/Mpc.  Then this galaxy ought to have a velocity away from us
of 1,000 km/s.  Okay, now actually MEASURE the velocity; suppose you
find v = 9,800 km/s.  The difference (-200 km/s, i.e. toward us)
is the 'peculiar velocity'.

  So, what Lauer and Postman did was to use their photometry to
estimate the distance of each galaxy (don't ask me how -- you'll have
to read their papers), and then compute the difference between
the expected Hubble flow at that distance and the actual measured
velocity.  

  If I remember correctly, what they found was that many galaxies,
over the entire area of their sample, had larger peculiar velocities
that we had thought; one implication is that there are large "bulk
flows" of many clusters of galaxies, all moving sort of in the same
direction.  This is a big surprise, because everyone thought that
there would be no such "bulk flows" over such large distances: the
common wisdom was that flows over smaller areas were possible, but that
on the large scales, local motions would average out.  

  So, the bottom line is, if Postman and Lauer are correct, then
we have to think hard to explain the large-scale bulk flows.  This
probably means thinking about the structure of the universe at early
times.  Since that's not my specialty, I'll stop here.

  Oh, and Postman and Lauer are both here at Princeton now, and tomorrow
(Tuesday, March 21) Marc will talk about these results.  If you're in
the neighborhood, stop by Peyton Hall at 4:20 and go to the auditorium --
the talk starts at 4:30.

--
-----                                                    Michael Richmond
"This is the heart that broke my finger."    richm...@astro.princeton.edu