Culture and Religion

A world view where the guide for society is based on human nature,
 not on ancient scriptures.  Home  or Topic Groups


Intergalactic Hydrogen Red Shift

This is a follow up to my post on 04/06 about a Quasar red shift where the large red shifts are not from the quasar itself.

From a paper from Caltech (linked below)

However, the vast majority of absorption lines in a typical quasar spectrum are ``intervening'', produced by gas unrelated to the quasar that is located along the line of sight between the quasar and the Earth.

A structure along the line of sight to the quasar can be described by its neutral Hydrogen column density, N(HI), the number of atoms per cm2. N(HI) is given by the product of the density of the material and the path length along the line of sight through the gas. Each structure will produce an absorption line in the quasar spectrum at a wavelength of lambda-obs = lambda-rest (1 + zabs), where zabs is the redshift of the absorbing gas and  lambda-rest = 1215.67 Angstroms is the rest wavelength of the Lyalpha transition. Since zabs < zQSO, the redshift of the quasar, these Lyalpha absorption lines form a ``forest'' at wavelengths blueward of the Lyalpha emission. The region redward of the Lyalpha emission will be populated only by absorption through other chemical transitions with longer lambda-rest. Historically, absorption systems with N(HI) < 1017.2 cm-2 have been called Lyalpha forest lines, those with 1017.2 < N(HI) < 1020.3 cm-2 are Lyman limit systems, and those with N(HI) > 1020.3 cm-2 are damped Lyalpha systems. The number of systems per unit redshift increases dramatically with decreasing column density, as illustrated in the schematic diagram in Figure 2. Lyman limit systems are defined by a sharp break in the spectrum due to absorption of photons capable of ionizing HI, i.e. those with energies greater than 13.6 eV.

This behavior of a red shift due to hydrogen in the line of sight to a distant object should apply to all distant objects, not just quasars.

This red shift is related to the hydrogen column density.

Is this absorption behavior by intergalactic hydrogen why all galaxies beyond our local group have red shifts?

I had questioned this observation in my post on 04/04 about the nearby Maffei galaxy group.


Hit back to go to previous page in history.
Here is the list of topics in this Cosmology Topic Group .

Ctrl + for zoom in;  Ctrl - for zoom out ;  Ctrl 0 for no zoom;
triple-tap for zoom to fit;  pinch for zoom change;  pinched for no zoom