AAS Meeting #193 - Austin, Texas, January 1999
Session 105. Galaxy Kinematics and Dynamics
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

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[105.10] Bulges of Spiral Galaxies: The Radial Distribution of their Stellar Population

P. Goudfrooij (STScI), P. Jablonka (Obs. de Paris/Meudon), J. Gorgas (U. Complutense, Madrid)

We show the first results of an extensive imaging and medium-resolution spectrophotometric survey of edge-on spirals to investigate radial population gradients in their bulge component (i.e., along their minor axis). Bulges of spiral galaxies constitute a main key to our understanding of the origin of the Hubble sequence. Located at the centers of spirals, they hold the signature of the sequence of formation ---outside-in or inside-out--- of the different sub-systems building a spiral galaxy: halo, disc, and bulge. The main goal of this proposal is to put significant constraints on current theories regarding bulge formation: (i)\/ Bulges form on short time scales (the dissipative collapse\/ scenario) versus (ii)\/ Bulges form from processed disk material through bar-driven re-distribution of angular momentum (the Secular Evolution\/ scenario). As to the latter scenario, models of mixing gas flows have shown that the radial abundance gradients are significantly reduced with respect to those in the dissipative collapse scenario (at a given bulge luminosity).

In this presentation, we will present first results of this survey. We will concentrate on Sa -- Sc galaxy types for which bulges stand out clearly. We have considered a suitable range in luminosity for each sub-type.

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