Gas kinetics in galactic disk. Why we do not need a dark matter to explain rotation curves of spirals?
Résumé
In present paper, we analyze how the physical properties of gas affect the Rotation Curve (RC) of a spiral galaxy. We confirm that the gas kinetics
must be taken into account to build an adequate model of a spiral galaxy. It is stressed, that while the inner part of the RC is subject of the Kepler law, for the correct description of the outer part of the RC, the collisional property of the gas should also be taken into account.
To confirm this fact we suggest both quantitative estimations and exact calculation to show how the outer part of the RC is related with the gas
density of the galactic disk. We argue that the hydrodynamic approach is not applicable for the correct modeling of large-scale gas kinematics of the galactic disk and more general diffusion equations should be used. Proposed calculations are based on solving both the Kepler's and the Fick equations and was carried out for two edge-on galaxies NGC7331 and NGC3198, for which the precise measurements of the gas column densities and RCs are available. An excellent coincidence between the measured column density of gas and that calculated from observed RCs is obtained.
From our result it follows, that if the gas density is high enough (more than 10(-5) cm(-3), the RC for the outer part of the disc is formed by
\textquotedblleft wind tails\textquotedblright\ of gas.
On the basis of the obtained result, we calculate the total masses of the NGC7331 and NGC3198. They consist 37.6x10(10)M\_sun and 7.7x10(10)M\_sun respectively. Consequences for cosmology are discussed.
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