The Cold Dark Matter Paradigm 21915
h18hh 21h^0h^312 h(^9) h
(^6) h
0.5 1 1.5 2
Lookback time (billions of years)
2.5 2.74 Gyr
Figure 9.4Zoom-in of the region of the sky showing galaxies observed by the SDSS Collab-
oration out to a radius of 2.74 Gyr [20]. The scorpion-like structure in the upper quadrant is
the Sloan Great Wall. From Gott III, J.et al., A Map of the Universe,Astrophys. J., 624 , 463,
published May 10 2005. © AAS. Reproduced with permission.
subsequently collapsed and disintegrated. Smaller structures and galaxies formed
later from the crumbs. But computer simulations of pancake formation and collapse
show that the matter at the end of the collapse is so shocked and so heated that the
clouds do not condense but remain ionized, unable to form galaxies and attract neu-
trino haloes. Moreover, large clusters (up to 10^14 푀⊙) have higher escape velocities,
so they should trap five times more neutrinos than large galaxies of size 10^12 푀⊙.This
scenario is not supported by observations, which show that the ratio of dynamic mass
to luminous mass is about the same in objects of all sizes, except for dwarf galaxies.
The ‘bottom–top’ scenario is supported by the observations that supergalaxies are
typically at distances푧≲ 0 .5, whereas the oldest objects known are quasars at redshifts
up to푧=5–7. There are also several examples of galaxies which are older than the
groups in which they are now found. Moreover, in our neighborhood the galaxies are
generally falling in towards the Virgo cluster rather than streaming away from it.
Several pieces of evidence indicate that luminous galaxies could have been assem-
bled from the merging of smaller star-forming systems before푧≈1. The Hubble Space
Telescope as well as ground-based telescopes have discovered vast numbers of faint