Shock-Heated Gas in the Large Scale Structure of the Universe

Cosmological shock waves are a ubiquitous consequence of cosmic structure formation. They play a major role in heating baryonic gas in the large scale structure of the universe. In this contribution we study the shock-heated gas in connection with shocks themselves, using a set of N-body/hydrodynamic simulation data of a ΛCDM universe. The distributions of shock speed and temperature of shock-hated gas both should reflect the depth of gravitational potential of associated nonlinear structures, so their morphology. From their distributions we find, in addition to hot gas in and around clusters/groups and warm-hot intergalactic medium (WHIM) with T = 10 − 10 K mostly in filaments, there is a significant amount of low temperature WHIM with T < 10 K distributed mostly as sheet-like structures. The low temperature WHIM was heated and collisionally ionized mainly by shocks with vsh . 150 km s , while photo-ionization by the UV and X-ray background radiations is important for metal ions. Not only the WHIM with T = 10 − 10 K but also the WHIM with T < 10 K make up a significant fraction of gas mass, implying the low temperature WHIM could be important in resolving the missing baryon problem. The shock-heated gas in filaments and sheets are manifested best through emissions and absorptions in soft X-ray and far UV. We confirm that the WHIM with T = 10− 10 K makes significant contributions to the soft X-ray background, absorptions of highly ionized species such as OVII and OVIII in AGN spectra, and line emissions from OVII and OVIII ions, as pointed by previous studies. However, the WHIM with T < 10 K is the major contributor to absorptions of lower ionized species such as OV and OVI, because these photo-ionized ions are most abundant in sheets of low density and temperature. On the contrary, lines of OV (630 Å) and OVI Department of Earth Sciences, Pusan National University, Pusan 609-735, Korea: [email protected] Department of Astronomy & Space Science, Chungnam National University, Daejeon 305-764, Korea: [email protected] Princeton University Observatory, Princeton, NJ 08544: [email protected] Korea Astronomy Observatory, Taejeon 305-348, Korea: [email protected]