Added WMAP7 parameters

[Roban]

Dear CosmoloPy community,

I've added a set of "WMAP 7 + BAO + H_0" parameters to the convenience
routines in parameters.py (from the Komatsu et al. paper of yesteday,
arXiv:1001.4538).

One small puzzle: The paper mentions that "'Redshift of
reionization' ... zreion ... values are somewhat different from those
in Table 1 of Komatsu et al. (2009b), largely because of the
changes in the treatment of reionization history in the Boltzmann code
CAMB (Lewis 2008)." Indeed, I could not match the WMAP7 optical depth
(tau) value using the WMAP7 zreion value, whereas I can match the
WMAP5 values by assuming helium is completely neutral [1]. I can't
match the WMAP7 value with either fully neutral, or singly-ionized
helium.

I'll have to look into what's going on in CAMB, but does anyone else
happen to know off the top of their heads?

-Roban

[1] see tests/test_wmap.py: http://github.com/roban/CosmoloPy/blob/master/cosmolopy/tests/test_wmap.py

See the changes made in this commit here:
http://github.com/roban/CosmoloPy/commit/2760ccf6e4cec808b4a85fc6fd24dc93ad0ad57f

P.S. Greetings from Zurich, where I've begun to settle into my new
position at ETH.

[Roban]

Okay, all is well. I have the answer (to the question of how CAMB
calculates tau given z_reion, and what changed from WMAP5 to WMAP7).

Apparently the CAMB used in WMAP 5 ignored helium in calculating
z_reion, as I said before. The CAMB used in WMAP 7 now assumes helium
ionizes once along with hydrogen, then is doubly ionized at z=3.5.
Adding that to the test_wmap.py code (which required some additions to
reionization.optical_depth_instant()) fixed the problem.

Note that optical_depth_instant does actually assume totally
instantaneous (step-function) re-ionization, while CAMB uses a tanh
function to model a continuous (but fast) transition. This makes only
a tiny difference in the optical depth or z_reion value, at least with
standard cosmologies [1], and I didn't see any need to bother
implementing such a physically-unmotivated function, but it would be
easy enough if anyone wants it.

-Roban

[1] Some useful notes on the CAMB formalism: http://cosmologist.info/notes/CAMB.pdf

The new commit is http://github.com/roban/CosmoloPy/commit/76f12205d3cbeea947ebdc9cbbe8b46aba4cf367

On Jan 28, 11:54 am, Roban <roba...@gmail.com> wrote:
> Dear CosmoloPy community,
>
> I've added a set of "WMAP 7 + BAO + H_0" parameters to the convenience
> routines in parameters.py (from the Komatsu et al. paper of yesteday,
> arXiv:1001.4538).
>
> One small puzzle: The paper mentions that "'Redshift of
> reionization' ... zreion ... values are somewhat different from those
> in Table 1 of Komatsu et al. (2009b), largely because of the
> changes in the treatment of reionization history in the Boltzmann code
> CAMB (Lewis 2008)." Indeed, I could not match the WMAP7 optical depth
> (tau) value using the WMAP7 zreion value, whereas I can match the
> WMAP5 values by assuming helium is completely neutral [1]. I can't
> match the WMAP7 value with either fully neutral, or singly-ionized
> helium.
>
> I'll have to look into what's going on in CAMB, but does anyone else
> happen to know off the top of their heads?
>
> -Roban
>

> [1] see tests/test_wmap.py:http://github.com/roban/CosmoloPy/blob/master/cosmolopy/tests/test_wm...
>
> See the changes made in this commit here:http://github.com/roban/CosmoloPy/commit/2760ccf6e4cec808b4a85fc6fd24...