Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008arep...52..257a&link_type=abstract
Astronomy Reports, Volume 52, Issue 4, pp.257-269
Astronomy and Astrophysics
Astronomy
3
98.52.Nr, 98.58.Db, 98.58.Ge, 98.62.Hr, 97.10.Bt, Spiral Galaxies, Molecular Clouds, H2 Clouds, Dense Clouds, And Dark Clouds, Hi Regions And 21-Cm Lines, Diffuse, Translucent, And High-Velocity Clouds, Spiral Arms And Bars, Galactic Disks, Star Formation
Scientific paper
The equilibrium thickness of the isothermal layers of interstellar gas and volume gas densities ρ gas in the plane of the disk as a function of galactocentric distance R are computed for seven spiral galaxies (including the Milky Way) using an axisymmetrical model. In this model, the thickness of the stellar disk varies with R and remains approximately equal to the minimum thickness of a stable equilibrium disk. We found the disk thickness to increase toward the periphery in at least five of the seven galaxies. The density of the stellar disk decreases with R faster than ρ gas , so that gas dominates at the disk peripheries in terms of density. A comparison of the azimuthally averaged star formation rate SFR and the gas density shows the absence of a universal Schmidt law SFR ˜ ρ {/gas n } for galaxies. However, the SFRs in various galaxies are better correlated with the volume than the gas surface density. The parameter n in the Schmidt law formally calculated using the least-squares method lies in the interval 0.8-2.4, being, on average, close to 1.5. The values of n calculated separately for the molecular gas display substantial scatter, but are, on average, close to unity. The value of n appears to increase with decreasing ρ gas , so that the fraction of gas that actively participates in star formation decreases with n.
Abramova O. V.
Zasov Anatoli V.
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