Evgenii O. Vasiliev

The simulation of molecular clouds formation in the Milky Way

Using 3D hydrodynamic calculations we simulate formation of molecular clouds in the Galaxy. The simulations take into account molecular hydrogen chemical kinetics, cooling and heating processes. Comprehensive gravitational potential accounts for contributions from the stellar bulge, two and four armed spiral structure, stellar disk, dark halo and takes into account self-gravitation of the gaseous component. Gas clouds in our model form in the spiral arms due to shear and wiggle instabilities and turn into molecular clouds after

Non-equilibrium ionization states and cooling rates of photoionized enriched gas

tsimgt 100

Evolution of multiple supernova remnants

Myr. At the times

Non-equilibrium cooling rate for a collisionally cooled metal-enriched gas

tsim 100 - 300

Giant molecular cloud scaling relations: the role of the cloud definition

Myr the clouds form hierarchical structures and agglomerations with the sizes of 100 pc and greater. We analyze physical properties of the simulated clouds and find that synthetic statistical distributions like mass spectrum, mass-size relation and velocity dispersion are close to those observed in the Galaxy. The synthetic

Extended O VI haloes of star-forming galaxies

l-v

Numerical code for multi-component galaxies: from N-body to chemistry and magnetic fields

(galactic longitude - radial velocity) diagram of the simulated molecular gas distribution resembles observed one and displays a structure with appearance similar to Molecular Ring of the Galaxy. Existence of this structure in our modelling can be explained by superposition of emission from the galactic bar and the spiral arms at

THE SIGNATURES OF PARTICLE DECAY IN 21 cm ABSORPTION FROM THE FIRST MINIHALOS

sim

Carbon Ionization States and the Cosmic Far-UV Background with He II Absorption

3-4 kpc.

Evolution of clustered supernovae

Non-equilibrium (time-dependent) cooling rates and ionization state calculations are presented for low-density gas enriched with heavy elements (metals) and photoionized by external ultraviolet/X-ray radiation. We consider a wide range of gas densities and metallicities and also two types of external radiation field: a power-law and an extragalactic background spectra. We have found that both cooling efficiencies and ionic composition of enriched photoionized gas depend significantly on the gas metallicity and density, the flux amplitude and the shape of ionizing radiation spectrum. The cooling rates and ionic composition of the gas in non-equilibrium photoionization models differ strongly (by a factor of several) from those in photoequilibrium due to overionization of the ionic states in the non-equilibrium case. The difference is maximal at low values of the ionization parameter and similar in magnitude to that between the equilibrium and non-equilibrium cooling rates in the collisionally controlled gas. In general, the non-equilibrium effects are notable at T ≲ 10 6 K. In this temperature range, the extent of mismatch between the two ionic states and their ratios between the photoequilibrium and the photo-non-equilibrium models reach a factor of several. The net result is that the time-dependent energy losses due to each chemical element (i.e. the contributions to the total cooling rate) differ significantly from the photoequilibrium ones. We advocate the use of non-equilibrium cooling rates and ionic states for gas with near-solar (and above) metallicity exposed to an arbitrary ionizing radiation flux. We provide a parameter space (in terms of temperature, density, metallicity and ionizing radiation flux), where the non-equilibrium cooling rates are to be used. More quantitatively, the non-equilibrium collisional cooling rates and ionization states are a better choice for the ionization parameter log U ≲ -5. The difference between the photoequilibrium and the photo-non-equilibrium decreases with the ionization parameter growth, and the photoequilibrium can be used for ionization parameter as high as log U ≳ -2 for Z ≲ 10 ―2 Z⊙ and log U ≳ 0 for Z ∼ Z ⊙ . Thus, the non-equilibrium calculations should be used for the ionization parameter range between the above-mentioned values. In general, where the physical conditions favour collisional ionization, the non-equilibrium (photo)ionization calculations should be conducted.