Multi-Spin Galaxies

Galaxies are the building blocks of the Universe: thus, in order to trace its evolution history one needs to understand how galaxies formed and evolved, in particular which are the main physical processes that have let to the observed structures.  The “classical” disk galaxies are made by stars, gas and dust which are distributed in a plane forming the disk: all these components co-rotating with the angular momentum vectors almost aligned.  A class of “peculiar” objects has also been observed, but significantly more rare than disk galaxies, that show a decoupled component of the angular momentum and so classified as “multi-spin galaxies” by V. Rubin in 1994. Up to date, this class of objects includes all galaxies with a kinematically distinct component of gas and/or stars, with several inclination angles and extensions with respect to the host galaxy: they are galaxies with extended polar rings/disks, inner polar disks, low-inclined rings, kinematically decoupled cores, and extended counter-rotating components. The observed phenomenon of warped gaseous and stellar disks is yet another example of misalignment between rotating components in a galaxy. Finally, recent findings show that even the Galaxy and M31  host a disk of satellites, possibly rationally supported, raising new questions and insights to the Λ-CDM models adopted in the “near-field cosmology.

Given that the decoupling of the angular momentum cannot be explained by the collapse of a single proto-galactic cloud, a “second event” need to be invoked in the formation history of the multi-spin galaxies, which could be galaxy-galaxy or galaxy-environment interactions. In the cold dark matter scenario for galaxy formation, such kind of gravitational interactions have played a fundamental role in defining the morphology of “normal” galaxies, in particular in the building up of spheroids: in this framework, the study of multi-spin galaxies, both at low and high redshift, can shed light on the main processes at work during galaxy interactions and on the influence of the environment. Moreover, the existence of two orthogonal components of the angular momentum in polar ring galaxies and the off-plane of gas in the warped disk galaxies, let these systems the ideal laboratory to study also the intrinsic shape of the dark matter halo. The question of the halo shape is important to constrain the dark matter models, through cosmological simulations which predict the distribution of the halo shapes and the universal radial mass density profile of the dark matter.

The conference will focus on the following topics:


  1. -Morphological and photometric properties of multi-spin systems: inner polar disks, polar rings/disks, warped host and inclined rings
  2. -Kinematic signatures of extraplanar rings/disks along the Hubble sequence
  3. -Relative frequency and the impact of environment
  4. -Sizes, luminosities, chemical abundances and masses of the decoupled components
  5. -Correlations of spin component properties
  6. -The Milky Way as a multi-spin galaxy
  7. -High z multi-spin systems


  1. -Density waves in counter-rotating stellar and gaseous disks
  2. -Time-scales and evolutionary paths: can we recognise transient features? Can we measure growth rates?
  3. -Warp structure & dynamics
  4. -Extreme warping
  5. -Star formation and stellar population of inclined and host rings/disks
  6. -Constraints on dark halos using extraplanar disks
  7. -Formation and evolution of inclined rings/disks