### 21-cm brightness temperature monopole from CAMB

Posted:

**October 22 2020**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 21-cm 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 21-cm 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.