21cm brightness temperature monopole from CAMB

 Posts: 2
 Joined: October 22 2020
 Affiliation: University of Copenhagen
21cm brightness temperature monopole from CAMB
Greetings!
I was wondering if it is possible to obtain the monopole of the brightness temperature (as a function of redshift) from CAMB. I am using the Python wrapper for CAMB.
My own attempt:
I have instructed CAMB to compute 21cm relevant observables with:
pars.Do21cm = True
pars.transfer_21cm_cl = True
Switching these on returns different transfer functions when I then
run get_matter_transfer_data() and get transfer functions out, so it is doing something.
I have found that the 4th transfer function that the command returns
is the "21 cm monopole source". It is indexed by redshift and
wavenumber. However, I have doubts that this is the right place to
be looking as I would not expect a monopole signal to need
information about the primordial power spectrum. I suppose this
transfer function is supposed to be multiplied by the power spectrum and then
integrated/summed.
I was wondering if it is possible to obtain the monopole of the brightness temperature (as a function of redshift) from CAMB. I am using the Python wrapper for CAMB.
My own attempt:
I have instructed CAMB to compute 21cm relevant observables with:
pars.Do21cm = True
pars.transfer_21cm_cl = True
Switching these on returns different transfer functions when I then
run get_matter_transfer_data() and get transfer functions out, so it is doing something.
I have found that the 4th transfer function that the command returns
is the "21 cm monopole source". It is indexed by redshift and
wavenumber. However, I have doubts that this is the right place to
be looking as I would not expect a monopole signal to need
information about the primordial power spectrum. I suppose this
transfer function is supposed to be multiplied by the power spectrum and then
integrated/summed.

 Posts: 1670
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: 21cm brightness temperature monopole from CAMB
Looks right to me.

 Posts: 2
 Joined: October 22 2020
 Affiliation: University of Copenhagen
Re: 21cm brightness temperature monopole from CAMB
Thank you, Antony!
To be sure:
 The documentation suggests that the transfer function $\Delta(k,z)$ comes out already divided by $k^2$.
 After multiplying by $k^2$ (in order to get the proper transfer function $\Delta(k,z)$) I then integrate the product of this transfer function (not its square) and the dimensionless primordial power spectrum $\mathcal P(k)$ such that the brightness temperature equals:
$T_b(z) = \int \mathrm{d}\log k \, \Delta(k,z) \mathcal P(k) $,
and it comes out in mK as long as I set pars.use_21cm_mK = True?
Please forgive the nonchalantreckless handling of the quantities. I am completely new to 21cm cosmology but more familiar with the CMB part of CAMB and wanted to try to out the 21 cm features of the code.
To be sure:
 The documentation suggests that the transfer function $\Delta(k,z)$ comes out already divided by $k^2$.
 After multiplying by $k^2$ (in order to get the proper transfer function $\Delta(k,z)$) I then integrate the product of this transfer function (not its square) and the dimensionless primordial power spectrum $\mathcal P(k)$ such that the brightness temperature equals:
$T_b(z) = \int \mathrm{d}\log k \, \Delta(k,z) \mathcal P(k) $,
and it comes out in mK as long as I set pars.use_21cm_mK = True?
Please forgive the nonchalantreckless handling of the quantities. I am completely new to 21cm cosmology but more familiar with the CMB part of CAMB and wanted to try to out the 21 cm features of the code.

 Posts: 1670
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: 21cm brightness temperature monopole from CAMB
Transfer functions should be squared for the power.