تسجيل الدخول

تسجيل

The Intergalactic Medium

المؤلف:  HOUJUN MO, FRANK VAN DEN BOSCH, SIMON WHITE

المصدر:  GALAXY FORMAT ION AND EVOLUTION

الجزء والصفحة:  p-13

2026-11-05

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The intergalactic medium (IGM) is the baryonic material lying between galaxies. This is and has always been the dominant baryonic component of the Universe and it is the material from which galaxies form. Detailed studies of the IGM can therefore give insight into the properties of the pregalactic matter before it condensed into galaxies. As illustrated in Fig. 1, galaxies do not evolve as closed boxes, but can affect the properties of the IGM through exchanges of mass, energy and heavy elements. The study of the IGM is thus an integral part of understanding how galaxies form and evolve. the properties of the IGM can be probed most effectively through the absorption it produces in the spectra of distant quasars (a certain class of active galaxies. Since quasars are now observed out to redshifts  beyond 6, their absorption line spectra can be used to study the properties of the IGM back to a time when the Universe was only a few percent of its present age.

Fig. 1. A flow chart of the evolution of an individual galaxy. The galaxy is represented by the dashed box which contains hot gas, cold gas, stars and a supermassive black hole (SMBH). Gas cooling converts hot gas into cold gas, star formation converts cold gas into stars, and dying stars inject energy, metals and gas into the gas components. In addition, the SMBH can accrete gas (both hot and cold) as well as stars, producing AGN activity which can release vast amounts of energy which affect primarily the gaseous components of the galaxy. Note that in general the box will not be closed: gas can be added to the system through accretion from the intergalactic medium and can escape the galaxy through outflows driven by feedback from the stars and/or the SMBH. Finally, a galaxy may merge or interact with another galaxy, causing a significant boost or suppression of all these processes