62 The First Gas Clouds [The image placed here in the print version has been intentionally omitted] Figure 3.4. The large-scale distributions of dark matter (left) and gas (right) in the IGM show a network of filaments and sheets, known as the "cosmic web." Overall, the gas follows the dark matter on large scales but is more smoothly distributed on small scales owing to its pressure. The snapshots show the projected density contrast in a 7 Mpc thick slice at zero redshift from a numerical simulation of a box measuring 140 comoving Mpc on a side. Figure