Direct Images of the Cosmic Web of Intergalactic and Circumgalactic Gas in the Distant Universe

Abstract

Most of the baryonic matter of the Universe resides in a highly-ionized gaseous intergalactic medium. This gas flows along dark-matter filaments toward galaxy superclusters, clusters, and groups until it pools around the galaxies into a circumgalactic medium. Eventually, the gas settles into the interstellar medium of the galaxies, where it fuels the successive generations of star formation that ultimately produce the stars and heavy elements that make up galaxies today. The gas has been studied for decades using absorption lines produced by Hydrogen and various ions of heavy elements in the spectra of background quasi-stellar objects (QSOs). But directly imaging the extremely faint glow of this "cosmic web" of intergalactic and circumgalactic gas has remained an elusive goal of observational cosmology. Some recent progress has been made by using imaging spectrographs to record high-redshift Ly$\alpha$ emission, although over only very narrow fields of view. Here we report direct images of intergalactic and circumgalactic gas in the distant Universe obtained using the Condor Array Telescope that we purposely built to reach extremely low-surface-brightness sensitivities over very wide fields of view. We show that these images directly detect and characterize the imprint of Ly$\alpha$ emission from the cosmic web at an overwhelming statistical significance. By stacking portions of the images centered on tens of thousands of galaxies of known redshift, we show that they also reveal extremely faint emission from H$^0$, C$^{3+}$, and Mg$^+$ and absorption from cosmic dust in the tenuous outskirts of the galaxies. Our results demonstrate that sensitive imaging observations can now detect and characterize emission (and absorption) from the cosmic web of intergalactic and circumgalactic gas (and dust).