Two-Zone IGM Model for the Global 21-cm Signal

To begin, first import ares:

import ares

To generate a model of the global 21-cm signal, we need to use the ares.simulations.Global21cm class. With no arguments, default parameter values will be used:

sim = ares.simulations.Global21cm()

See the Parameters page for a listing of parameters that can be passed to ares.simulations.Global21cm as keyword arguments.

Since a lot can happen before we actually start solving for the evolution of IGM properties (e.g., initializing radiation sources, tabulating the collapsed fraction evolution and constructing splines for interpolation, tabulating the optical depth, etc.), initialization and execution of calculations are separate. To run the simulation, we do:

sim.run()

The main results are stored in the attribute sim.history, which is a dictionary containing the evolution of many quantities with time. To look at the results, you can access these quantities directly:

import matplotlib.pyplot as pl

pl.plot(sim.history['z'], sim.history['dTb'])

Or, you can pass the Global21cm instance to an analysis class, which contains convenience routines for common plots of interest:

anl = ares.analysis.Global21cm(sim)
ax = anl.GlobalSignature()

One possible realization for the global 21-cm signal.

If you’d like to save the results to disk, do something like:

sim.save('test_21cm')

which saves the contents of sim.history at all time snapshots.

Note

The default format for output files is pkl, though ASCII (e.g., .txt), .npz, and .hdf5 are also supported. Use the optional keyword argument suffix.

To read results from disk, you can supply a filename to ares.analysis.Global21cm rather than a ares.simulations.Global21cm instance if you’d like, e.g.,

anl = ares.analysis.Global21cm(history='test_21cm.pkl')

See Built-In Analysis Tools for more information about readily available analysis routines.

DIY Parameter Study

To do simple parameter study, you could do something like:

ax = None
for fX in [0.2, 1.]:
    for fstar in [0.05, 0.1]:
        sim = ares.simulations.Global21cm(fX=fX, fstar=fstar)
        sim.run()

        # Object for common analysis routines
        anl = ares.analysis.Global21cm(sim)

        # Plot the global signal
        ax = anl.GlobalSignature(ax=ax,
            label=r'$f_X=%.2g, f_{\ast}=%.2g$' % (fX, fstar))


ax.legend(loc='lower right', fontsize=14)
pl.draw()

Four realizations of the global 21-cm signal, varying the normalization of the \(L_X\)-SFR relation and the star formation efficiency.

See Simple Parameter Study for examples of how to run and analyze large grids of models more easily.