Shock‐heated Gas in the Large‐Scale Structure of the Universe

Cosmological shock waves play a major role in heating baryonic gas in thelarge scale structure of the universe. In this contribution we study theshock-heated gas in connection with shocks themselves. The distributions ofshock speed and temperature of shock-hated gas both should reflect the depth ofgravitational potential of associated nonlinear structures, so theirmorphology. From their distributions we find, in addition to hot gas in andaround clusters/groups and warm-hot intergalactic medium (WHIM) withT=10^5-10^7 K mostly in filaments, there is a significant amount of lowtemperature WHIM with T < 10^5 K distributed mostly as sheet-like structures.Not only the WHIM with T=10^5-10^7 K but also the WHIM with T < 10^5 K make upa significant fraction of gas mass, implying the low temperature WHIM could beimportant in resolving the missing baryon problem. The shock-heated gas infilaments and sheets are manifested best through emissions and absorptions insoft X-ray and far UV. We confirm that the WHIM with T=10^5-10^7 K makessignificant contributions to the soft X-ray background, absorptions of highlyionized species such as OVII and OVIII in AGN spectra, and line emissions fromOVII and OVIII ions, as pointed by previous studies. However, the WHIM with T <10^5 K is the major contributor to absorptions of lower ionized species such asOV and OVI, because these photo-ionized ions are most abundant in sheets of lowdensity and temperature. (abridged)