Has anyone estimated the mass of those hydrogen clouds?
Many (most?) are believed to be proto-galaxies, and so are enormous in scale.
“We hypothesize that a lyman alpha cloud does not need to transport angular momentum outward as it collapses to form a galaxy with a flat rotation curve, M_interior \propto R. A cloud with uniform density and solid-body rotation naturally has the angular momentum distribution of a disk with a flat rotation curve, so the cloud should be able to collapse to a spiral galaxy while conserving the angular momentum and radial ordering of all mass elements. To test this hypothesis, we will use a simplified nbody + hydrodynamics code which can rigorously banish all transfer of angular momentum while still preserving the essential features of dissipative baryonic collapse.”
http://flux.aps.org/meetings/YR02/APR02/baps/abs/S6260005.html
Also see:
http://markelowitz.com/cosmology.htm
>Has anyone estimated the mass of those hydrogen clouds?
Q- How dense are the Lyman alpha forest systems (column densities)?
A- 1014 atoms per square centimeter. Lyman limit systems are 103 times denser and damped Lyman alpha systems another factor of 103 times more.
http://astro.berkeley.edu/~jcohn/lya.html
Lyman-alpha forest
From Wikipedia, the free encyclopedia
In astronomical spectroscopy, the Lyman alpha forest is the sum of absorption lines arising from the Lyman alpha transition of the neutral hydrogen in the spectra of distant galaxies and quasars.
These absorption lines result from intergalactic gas through which the galaxy or quasar’s light has travelled. Since the absorption and emission of light follow the laws of quantum mechanics, only photons with specific energies can be absorbed. This causes each individual absorption line. The forest is created by the fact that photons that come to us from distant light sources show Hubble redshift that depends on the distance between us and the source of light.
Since neutral hydrogen clouds at different positions between Earth and the distant light source see the photons at different wavelengths (due to the redshift), each individual cloud leaves its fingerprint as an absorption line at a different position in the spectrum as observed on Earth.
The Lyman alpha forest is an important probe of the intergalactic medium and can be used to determine the frequency and density of clouds containing neutral hydrogen, as well as their temperature. Searching for lines from other elements like helium, carbon and silicon (matching in redshift), the abundance of heavier elements in the clouds can also be studied. A cloud with a high column density of neutral hydrogen will show typical damping wings around the line and is referred to as a damped Lyman alpha system.
For quasars at higher redshift the number of lines in the forest is higher, until at a redshift of about 6, there is so much neutral hydrogen in the intergalactic medium that the forest turns into a Gunn-Peterson trough. This shows the end of the reionization of the universe.
http://en.wikipedia.org/wiki/Lyman-alpha_forest