Lying at the centre and denser regions of galaxies, bulges are a keystone in our understanding of galaxy formation and evolution. It is also their location, shared with other components of galaxies what makes them so difficult to study. In this review I have tried to provide an overview of the main kinematic features observed in extragalactic bulges.
Identifying the formation scenario for bulges based solely on kinematic grounds is a very difficult task. The orbits of the different structural components in galaxies (e.g. bulges, disks, bars, spiral arms, nuclear disks rings, etc) are not necessarily well separated in phase-space. The best example of this complexity come from the observations of the Milky Way bulge. As nicely illustrated in other contributions to this volume (e.g. González & Gadotti, or Sánchez-Blázquez), the combined study of kinematics and stellar populations provides one of the best ways to discern between different formation scenarios. While this coupling can be achieved relatively easy in the Milky Way (because it is possible to measure the properties of individual stars) this is no easy task in bulges of other galaxies where all we get is the integrated light along the line-of-sight. Fortunately, with better data, models, and numerical tools we are at the verge of being able to treat other galaxies in the same way we study our own Galaxy. Studies of the coupling between kinematics and stellar populations in external galaxies are now flourishing (e.g. Ocvirk et al., 2008). Initially restricted to galaxies with known distinct counter-rotating components, they are now exploring more regular galaxies (e.g. Johnston et al., 2014).
As remarked many times throughout this review, this new step in the 3D decomposition of galaxies can only be achieved with datasets that allow the uniform exploration of galaxies in the two-dimensions they project in the sky. The first generation of IFU surveys and instruments (e.g. SAURON, ATLAS3D, DiskMass, SINFONI, VIMOS, PPaK) showed us the potential of these datasets to reveal the intrinsic properties of galaxies. The currently ongoing IFU surveys (e.g. CALIFA, SAMI, MaNGA, KMOS3D) will allow the exploitation of these new techniques for very large, morphologically and mass unbiased samples of galaxies. We should not forget though that we can still learn a lot of the physical processes governing galaxies, and bulge formation and evolution in particular, with unique instruments like MUSE. The Milky Way is a unique case, as we will be able to probe the 3D nature of the Galaxy directly thanks to the Gaia space mission.
Acknowledgements J. F-B would like thank D. Gadotti, E. Laurikainen and R.F. Peletier for their invitation to take part in this volume and for their infinite patience waiting for this review. J. F-B acknowledges support from grant AYA2013-48226-C3-1-P from the Spanish Ministry of Economy and Competitiveness (MINECO), as well as from the FP7 Marie Curie Actions of the European Commission, via the Initial Training Network DAGAL under REA grant agreement number 289313.