Infall and Omega

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Last time we discussed a simple two-body case of gravitational infall
from which OMEGA could be recoverd via

under the condition that the two bodies are isolated. This analysis
leads to low OMEGA. A more proper treatment of the problem uses
a non-linear approximation which works for higher values of
* delta rho/rho *.

For OMEGA = 1 non-linear approximatation recovers * delta rho/rho *
~ 4.5 for * delta v/v * = -1 for OMEGA = 1. The previous
equation recovers this with * delta rho/rho * = 3 and that's
incorrect. (* delta rho/rho * = 4.5 can be derived analytically
for the OMEGA = 1 case)

Last time we considered this cartoon:

To recover the observed CBR Dipole Anisotropy requires that there
is more than just Virgo which is gravitationally accelerating
the Local Group. The nearest other region of mass over density
is the Hydra-Centaurus Supercluster. This is shown below:

The spatial distribution of catalog galaxies. The diagonal band
containing lots of points is called the Supergalactic Plane and
it may be a very large structure.

The simplest approximation to assume that HC is at rest and is
perturbing both our motion as well as the entire Local Supercluster.

But, in 1986 it was announced that HC itself was moving. This
was the beginning of the quest for the Great Attractor.

Searching for the Great Attractor

Astrophysical Journal Paper

Another indicator that the flow declines to zero at v ~ 6000 km/s
(from Giovanelli \etal 1996)

Ultimately the aim is to infer the large scale gravitational field from
the large scale density field. This method is known as POTENT and
is illustrated below:

The Electronic Universe Project
e-mail: nuts@moo.uoregon.edu