The Formation and Evolution of Exponential Disks in Galaxies

Exponential stellar disks are ubiquitous. The stars in both spiral and dwarf galaxies are generally found to be organized in exponential disks, even to very low surface densities and in both stellar dominated and gas dominated galactic environments. But why is this? The associated gas disks do not fall off with radius in the same manner. Furthermore, star formation is highly lumpy. How does lumpy star formation produce distributions of stars that fall off smoothly. And how are these profiles maintained over many Gyr?

In addition, abrupt breaks in the stellar surface brightness or density profiles are also common: the stars follow an exponential in the inner part of the galaxy and an exponential with a different slope in the outer galaxy. In spiral galaxies there seems to be a change in the stellar populations at the break, but in dwarf galaxies the break remains in the stellar mass density profile. So what happens at the break in these galaxies? Here we bring together theorists and observers to discuss the formation of exponential disks and their evolution.

This workshop aims to address the following fundamental questions:

  • Why are exponential disks formed?
  • Are dwarf disks the same as spiral disks?
  • What maintains exponential disks once formed? What role, if any, does star formation play in maintaining the exponential disk? Or are other processes continuously adjusting the profile independent of star formation? Is this the same in spirals and dwarfs?
  • Why do spiral disks evolve inside-out and dwarf disks form outside-in?
  • For galaxies with breaks in their stellar surface brightness or mass profiles, what happens at the break?