Generation of Primordial Magnetic Fields

Color GIF version of plates:
Figure 4
Figure 5
Figure 7a
Figure 7b
Figure 9a
Figure 9b

Explanation

Evolution of a thin slice of the universe as a function of time (represented as a scale factor a). The evolution starts at z~20 (a~0.05) and stops at z=4 (a=0.2) (the last movie stops at z=5). The respective panels show:
• upper left: hydrogen neutral fraction, stretch from 10^-5 (black) to 1(pink); ionization fronts come out red.
• lower left: gas density in units of average cosmic density, stretch from 10^-1(black) to 10²(pink) (10³ in the second movie);
• lower right: gas temperature in K, stretch from 10³(black) to 10⁵(pink) (10^5.5 in the second movie);
• upper left: magnetic field strength in gauss, stretch from 10^-22(black) to 10^-18(pink) (10^-20.5 in the third movie);

  The value of the scale factor a is also shown in the middle bar.

  The Biermann battery is the most efficient when the temperature gradient is perpendicular to the gradient of the electron density. We identified two arrangements, when this is indeed the case: when an I-front breaks through a neutral halo of a star-forming object (the second movie and an accompanying cartoon), and when an I-front goes across a filament (the third movie and an accompanying cartoon).

Explanation

The upper right panel shows the magnetic field strength, just like in the movies. The other three panels show B_x, B_y, and B_z in the following stretch:
stretch = sign(B_i) lg(1+10²²|B_i|).
Thus, +3 corresponds to B_i=10^-19G, and -3 corresponds to B_i=-10^-19G.