Size of the Thermal Source in Relativistic Heavy-Ion Collisions

The dependence of the size of the thermal source on centrality in ultrarelativistic heavy-ion collisions is studied. The interaction region consists of a well defined thermalized core, and of an outer mantle where the production scales with the number of participants. The thermal source builds up in the region with the largest density of participants in the transverse plane. Particle production in the thermalized core is enhanced in comparison to the wounded nucleon model. The change of the degree of strangeness saturation with centrality is also discussed. We perform an estimate of high p? jet absorption finding that an increase of the absorption in the thermal core is compatible with the data. (author)