Simple Models 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 (see Field Listing for more information on what’s available). 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 access convenience routines within the analysis class, which is inherited by the ares.simulations.Global21cm class:

sim.GlobalSignature()
http://casa.colorado.edu/~mirochaj/docs/ares/basic_21cm.png

One possible realization for the global 21-cm signal. You should get something that looks like this, but may not be exactly the same depending on what version of ares you’re using.

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 to the file test_21cm.history.pkl and the parameters used in the model in test_21cm.parameters.pkl.

Note

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

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

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

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, problem_type=101)
        sim.run()

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


ax.legend(loc='lower right', fontsize=14)
pl.draw()
http://casa.colorado.edu/~mirochaj/docs/ares/ares_simple_param_study.png

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

Check out Population Parameters for a listing of the most common parameters that govern the properties of source populations, and Simple Parameter Study: 2-D Model Grid for examples of how to run and analyze large grids of models more easily. The key advantage of using the built-in model grid runner is having ares automatically store any information from each calculation that you deem desirable, and store it in a format amenable to the built-in analysis routines.