Baryons at low density: stellar halos around galaxies

Stellar halos are ubiquitous in luminous galaxies, but because of their faint surface brightness the detailed study of their physical properties has been difficult and, until recently, confined largely to the Milky Way (MW) and Andromeda. Since the advent of large cameras and surveys, both from ground and space, our knowledge of stellar halos is increasing. Several late and early-type galaxies had stellar halo properties traced out to hundred kiloparsecs or beyond, revealing very low luminosity extended stellar structures similar to halos of our own MW and our closest neighbor, the Andromeda galaxy.

Observations show that these halos have complex morphologies with multiple stellar components, complex kinematics and substructures that indicate past history of mergers. These morphologies resemble the density maps from cosmological simulations of galaxy formation in a hierarchical universe and a large amount of effort is invested to try to understand how we go from a qualitative resemblance to quantitative measurements and frequencies of these substructures.

This workshop  will bring together theorists and observers to discuss the results from the space and ground-based surveys of stellar halos in disks and ellipticals as well as from simulations. The properties of the Milky Way halo will also be discussed as representative of those of a halo around a spiral disk galaxy, with the main focus of the workshop being on extragalactic stellar halos. The aim is to review our knowledge (or lack thereof) about the physical properties of stellar halos and their origin in the context of cosmological predictions.