Testing Global Ism Models: a Detailed Comparison of Ovi Column Densities with Fuse and Copernicus Data

We study the OVI distribution in space and time in a representative section of the Galactic disk by 3D adaptive mesh refinement HD and MHD simulations of the ISM, including the disk-halo-disk circulation. The simulations describe a supernova driven ISM on large (∼ 10 kpc) and small (∼ 1.25 pc) scales over a sufficiently large timescale (∼ 400 Myrs) in order to establish a global dynamical equilibrium. The OVI column density, N(OVI) , is monitored through lines of sight measurements at different locations in the simulated disk. One has been deliberately chosen to be inside of a hot bubble, like our own Local Bubble, while the other locations are random. We obtain a correlation between N(OVI) and distance, which is independent of the observer’s vantage point in the disk. In particular, the location of the observer inside a hot bubble does not have any influence on the correlation, because the contribution of an individual bubble (with a typical extension of 100 pc) is negligibly small. We find a remarkable agreement between the OVI column densities (as a function of distance) and the averaged OVI density (∼ 1.8× 10−8 cm−3) in the disk from our simulations and the values observed with COPERNICUS, and FUSE. Our results strongly support the important rôle of turbulent mixing in the distribution of OVI clumps in the ISM. Supernova induced turbulence is quite strong and unavoidable due to shearing motions in the ISM and operates on a large range of scales. Subject headings: Hydrodynamics – Magnetohydrodynamics – Galaxy: disk – ISM: general – ISM: kinematics and dynamics – ISM: structure