Annular Structure Analysis of the Starburst Spiral Galaxy NGC 7217

Summary

Circumnuclear starbursts can occur in galaxies with no notable companions. One of the consequences of this mechanism is to sweep out the star-forming gas from the few inner kiloparsec around the nucleus causing annular structures. Repeated starbursts (and perhaps the initial starburst itself) require a mechanism to feed new gas towards the axis of rotation. A dynamical process for this refuelling is based on the effects of departures from axisymmetry in the gravitational potential of the bulge, which can cause a net gaseous inflow, seen at its densest along a bar or bar-like structure, but also present for more generalized oval distortion. In an initial phase of the present work we have analysed the bulge component of a sample of spiral galaxies obtained using the 4.2-m WHT and the 2.5-m INT at the Observatorio del Roque de los Muchachos (La Palma). These galaxies present a starburst signature or exhibit evidence of residual phenomena from a previous starburst (see Beckman et al. 1991; Varela 1992). Seeing values oscillated between 0″·5 to 1″·4. Data reduction was performed using FIGARO and IRAF standard programs. We carried out a photometric analysis which enable us to perform a bulge/disc emission decomposition, in order to reconstruct that associated only with the bulge (Prieto et al. 1992a,b; Varela 1992).