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trinitree88
2010-Mar-19, 03:43 PM
The origin of the extragalactic cosmic gammma ray background has been a mystery. The latest data from Fermi indicates that a large number of faint normal galaxies is the cause rather than a smaller number of extreme ones. SEE: Fields et al :http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.3647v1.pdf

Jerry
2010-Mar-20, 10:06 PM
The background is just more of the same? How boring is that? There are a couple of parallel papers dealing with aging, or rather the lack of it, in the galactic sample of redshifts from ~ 2 to 6.


This implies that the total number of resolved galaxies will remain small, and thus that the bulk of the star-forming universe will continue to be unresolved and thus contribute to the Fermi EGB. This contrasts sharply with the situation for blazars, for which the many new resolved objects substantially reduce the unresolved EGB contribution. Therefore, we predict that as Fermi sensitivity increases, a star-formation-dominated EGB will remain essentially unchanged despite the identification of additional faint point sources.


Our buddy Martin archived a paper a few weeks ago:

http://xxx.lanl.gov/abs/1002.0525

Angular size test on the expansion of the Universe


Assuming the standard cosmological model as correct, the average linear size of galaxies with the same luminosity is six times smaller at z=3.2 than at z=0, and their average angular size for a given luminosity is approximately proportional to 1/z. Neither the hypothesis that galaxies which formed earlier have much higher densities nor their luminosity evolution, mergers ratio, or massive outflows due to a quasar feedback mechanism are enough to justify such a strong size evolution...

...One of the models explored, a very simple phenomenological extrapolation of the linear Hubble law in a Euclidean static universe, fits the angular size vs. redshift dependence quite well, which is also approximately proportional to 1/z with this cosmological model. There are no free parameters derived ad hoc, although the error bars allow a slight size/luminosity evolution. The type Ia supernovae Hubble diagram can also be explained in terms of this model with no ad hoc fitted parameter.

This sounds awfully ATM; I mean, for goodness sake, 1/z is exactly what a steady-state universe would look like; and this is observational evidence! But Lopez-Corredoira includes an unusual warning in his abstract:


WARNING: I do not argue here that the true Universe is static. My intention is just to discuss which theoretical models provide a better fit to the data of observational cosmology.
Oh good thing he warned us. That would be heratical!

TheHalcyonYear
2010-Mar-20, 10:36 PM
. . .


WARNING: I do not argue here that the true Universe is static. My intention is just to discuss which theoretical models provide a better fit to the data of observational cosmology.

Oh good thing he warned us. That would be heratical!
I may get an infraction for moderating which is definitely my place here, but I ask:

Why do you do this Jerry? Now here is someone who, to this point, has stated that they are only looking to stack theoretical models against observational data in order to characterize fits. This seems a reasonable academic exercise for understanding both the models and the data. However, you have to make sarcastic comments and characterize the discussion as ATM. This can only discourage participation in and dampen interest in such a conversation while polarizing the entire thread.