IAU Symposium Abstract S186-085P

Surface Brightness Gradients Produced by the Ring Waves of Star Formation

Korchagin1,Y. Mayya2,E. Vorobyov1 & A. Kembhavi3
1 Institute of Physics, Stachki 194, Rostov-on-Don, Russia < vik@rsuss1.rnd.runnet.ru >
2 Tata Institute, Bombay, India < ydm@tifrvax.tifr.res.in >
3 I.U.C.A.A., Pune, India < akk@iucaa.ernet.in >

Using stellar evolutionary and stellar atmospheric models we calculate surface brightness gradients in starburst galaxies with the outwardly propagating waves of star formation. We consider the two possible mechanisms for the formation of the star burst outer rings - the self-induced wave and the density wave radially propagating in the gaseous disk. The results of our computations show that the surface brightness gradients produced in both scenario of star formation does not differ significantly but strongly depend on the velocity of the wave of star formation and on the initial mass function of stars. We compare the results of our computations with the optical properties of the galaxy A0035-335 (the Cartwheel galaxy) and the VIIZw466 ring system. The best fit to the the observed radial $ H\alpha$ surface brightness distribution in the Cartwheel have been obtained if the velocity of the wave of star formation is about 90 km/s. The red continuum brightness distribution in the Cartwheel indicates however that the outer ring of star formation is not the first star forming event in the history of the Cartwheel, and that the wave of star formation propagates on a pre-existing stellar disk. The surface brightness distribution in the VIIZw466 matches very well to the properties of the stellar populations produced by the wave of star formation propagating in a purely gaseous disk. We conclude that VIIZw466 is probably experiensing the first event of star formation in the disk.