The 21cm global signal and 3D power spectrum from the dark ages
Posted: November 20 2022
We have been using CAMB, and have several questions about getting from it the 21-cm global signal and the 21-cm power spectrum during the dark ages.
How do we get the 21-cm global signal (i.e., mean 21-cm brightness temperature) T_b as a function of redshift directly from CAMB? We can get it indirectly by running once with use_21cm_mK = True and once with use_21cm_mK = False, and taking the ratio of the monopole transfer functions in the two cases. Is there a better way?
The 21-cm power spectrum: Our aim is to generate the (total) 21-cm power spectrum P(k) and its angular decomposition terms P_mu^0, P_mu^2, and P_mu^4 using CAMB. We find the following possibly relevant parameters for 21cm. Please let us know if we missed anything. Other parameters are kept at their default values.
• WantCls – (False)
• Do21cm – (True)
• Evolve_baryon_cs – (boolean) Evolve a separate equation for the baryon sound speed rather than using background approximation
• Evolve_delta_xe – (boolean) Evolve ionization fraction perturbations
• Evolve_delta_Ts – (boolean) Evolve the spin temperature perturbation (for 21cm)
• line_phot_dipole – (boolean) Dipole sources for 21cm
• line_phot_quadrupole – (boolean) Quadrupole sources for 21cm
• line_basic – (boolean) Include main 21cm monopole density/spin temperature sources
• line_distortions – (boolean) Redshift distortions for 21cm
• line_extra – (boolean) Include other sources
We set Evolve_baryon_cs and Evolve_delta_xe to True, but we are not sure about Evolve_delta_Ts. We ran CAMB with Evolve_delta_Ts=False and with Evolve_delta_Ts=True. We found that the monopole transfer functions are the same for both cases. However, we found that the run time for Evolve_delta_Ts=True is 2 orders of magnitude higher than for the Evolve_delta_Ts=False case. Does this make sense?
We have a fundamental question: Does Transfer_monopole for the 21-cm monopole transfer function give P_mu0 ~ (Transfer_monopole)^2, i.e., the 21-cm power spectrum without the velocity effect? Is there a way to get from CAMB the total 21-cm power spectrum including the velocity effect?
We also set line_basic to True, and varied line_phot_dipole, line_phot_quadrupole, line_distortions, and line_extra. But, we found that the monopole transfer function does not depend on these parameters. Are any of them relevant to us, or do they all have an insignificant effect?
Thanks for any help.
How do we get the 21-cm global signal (i.e., mean 21-cm brightness temperature) T_b as a function of redshift directly from CAMB? We can get it indirectly by running once with use_21cm_mK = True and once with use_21cm_mK = False, and taking the ratio of the monopole transfer functions in the two cases. Is there a better way?
The 21-cm power spectrum: Our aim is to generate the (total) 21-cm power spectrum P(k) and its angular decomposition terms P_mu^0, P_mu^2, and P_mu^4 using CAMB. We find the following possibly relevant parameters for 21cm. Please let us know if we missed anything. Other parameters are kept at their default values.
• WantCls – (False)
• Do21cm – (True)
• Evolve_baryon_cs – (boolean) Evolve a separate equation for the baryon sound speed rather than using background approximation
• Evolve_delta_xe – (boolean) Evolve ionization fraction perturbations
• Evolve_delta_Ts – (boolean) Evolve the spin temperature perturbation (for 21cm)
• line_phot_dipole – (boolean) Dipole sources for 21cm
• line_phot_quadrupole – (boolean) Quadrupole sources for 21cm
• line_basic – (boolean) Include main 21cm monopole density/spin temperature sources
• line_distortions – (boolean) Redshift distortions for 21cm
• line_extra – (boolean) Include other sources
We set Evolve_baryon_cs and Evolve_delta_xe to True, but we are not sure about Evolve_delta_Ts. We ran CAMB with Evolve_delta_Ts=False and with Evolve_delta_Ts=True. We found that the monopole transfer functions are the same for both cases. However, we found that the run time for Evolve_delta_Ts=True is 2 orders of magnitude higher than for the Evolve_delta_Ts=False case. Does this make sense?
We have a fundamental question: Does Transfer_monopole for the 21-cm monopole transfer function give P_mu0 ~ (Transfer_monopole)^2, i.e., the 21-cm power spectrum without the velocity effect? Is there a way to get from CAMB the total 21-cm power spectrum including the velocity effect?
We also set line_basic to True, and varied line_phot_dipole, line_phot_quadrupole, line_distortions, and line_extra. But, we found that the monopole transfer function does not depend on these parameters. Are any of them relevant to us, or do they all have an insignificant effect?
Thanks for any help.