pmfs

Data and code accompanying Gluscevic et al. (2016a). The code in this repository can be used to:

• Calculate the effect of cosmological magnetic fields on 21-cm brightness-temperature fluctuations
• Forecast sensitivities of 21-cm tomographic surveys to detecting cosmological magnetic fields, using the new method proposed in this series of papers

Data

Figures in the paper use outputs of 21CMFAST code that are in code/inputs and outputs of the CAMB code in code/matter_power. Numerical results represented in our Figures are in code/results.

Dependencies

This code will only work for python 2. For calculations, you will need:

• basic python scientific packages contained within the Anaconda python distribution (numpy, scipy, matplotlib)
• cosmolopy
• numba

To reproduce our Fig. 2, you will also need Healpix and Healpy (see here).

Usage

There are three main scripts you may want to use and can import from python command line:

• fisher.py: Enables computation of the detection threshold for a given 21-cm survey (note: only implemented for an array of dipoles in a compact-grid configuration). The main routines are:

  • rand_integrator: It takes on input zmin, zmax, Omega_survey (sr), and Delta_L (km) of the survey. For default values, it will give you the first data point of Fig. 5 for the uniform-field case. If you set mode='xi', it will give you the first data point of Fig. 4 for fiducial model. One call takes a few mins with default parameters.
  • calc_SNR: It takes the same survey parameters as rand_integrator. If you use default parameters, you will get the first data point of Fig. 5 for the SI case ($A_0$ corresponding to that point). One call takes about 10mins with default parameters.

• plots_pmfs.py: If you are looking to use this module to reproduce Figures in the paper, you will need this routine and you can read code/plotting_commands_for_paper.txt on how to use it to do that. Note that the plotting routine that produces Figs. 4 and 5 (the main result of the paper) is grid_DeltaL, and it requires that you first compute sensitivities for a range of maximum baselines, using appropriate routines of fisher. The format of the inputs to the plotting routine is as contained in code/results/midFSTAR, code/results/loFSTAR, and code/results/hiFSTAR. You can also just run the plotting routine on our numerical results (they are in results) to get the figures.

• pmfs_transfer.py: This module contains a basic implementation of the brightness-temperature calculation. The main routines are:

  - ``calc_Tb``: implementation of Eq. (1) (computation of the brightness-temperature fluctuation in presence of a magnetic field) 
  - ``calc_G``: implementation of Eq. (24) (the corresponding transfer function)
  

  Both routines take on input: - values of $x_{\alpha,(2)}$, $x_{c,(2)}$, and $x_B$ (all are functions of redshift; see the paper for definitions), - coordinates of the wavevector $\vec k$ and the line of sight $\widehat n$ (both in the frame where the magnetic field is along the z axis; angle coordinates are in radians), while the second routine also takes spin and CMB temperatures at a given redshift (in Kelvin).

This should get you quickly started if you wish to reproduce our results; for more details, see documentation within the source code and in the paper.

Additional notes

• If you wish to parallelize your sensitivity calculation, check out code/cluster_commands_for_paper.txt and code/cluster_runner.py for inspiration.

• Code for lensing-noise calculation of Appendix B is in code/lensing-code; see README there for more information.

Attribution

If you use this code, please cite Gluscevic et al. (2016a) and Venumadhav et al (2014).