PROFESSOR ANVAR SHUKUROV

The interstellar medium (ISM) in spiral galaxies is a site of turbulent dynamo action that produces both large-scale and small-scale magnetic fields. This is an unusual dynamo system, since the ISM is highly inhomogeneous: three pervasive gas phases are identified as (1) the hot, dilute gas, (2) warm, partially ionized gas and (3) cool, dense gas clouds. The hot gas is fully ionized; it occupies about 20% of the volume near the galactic midplane. Most of the ISM volume (80%) is occupied by the warm gas, whereas the gas clouds have a negligible volume fraction but contain 90% of the gas mass. This complex structure is produced by energy injection from supernova stars that also drive a system of random shock fronts travelling through the ISM. We discuss properties of the mean and random magnetic fields in the multi-phase ISM, as obtained from fully nonlinear, non-ideal MHD simulations. Magnetic and velocity fields are separated into the mean and random parts using Gaussian smoothing adapted to satisfy the Reynolds rules of averaging. The correlation properties of magnetic, velocity and density fields in each phase, and their variation with position above the galactic midplane, are presented, compared and discussed. In order to identify the phase(s) that hosts the mean-field and fluctuation dynamos, we derive and analyse the probability distributions of magnetic line lengths in the ISM phases, for both the mean and random magnetic fields. For the first time, we have obtained conclusive and quantitative evidence that the mean-field dynamo resides in the warm phase of the ISM. We discuss advanced methods of statistical analysis of intermittent random fields based on integral geometry and computational topology (e.g., Betti numbers and persistence diagrams).