GeminiFocus October 2018 | Page 11

Dwarfs Emerge from the Tidal Debris of Interacting Galaxies Large galaxies are produced through the merging or accretion of smaller galaxies. If the merging galaxies contain enough gas- eous material, a burst of star formation may cause the stellar mass of the final galaxy to be substantially larger than the combined mass of the stars of the two original galaxies. This is the basis of hierarchical structure for- mation, the standard paradigm in the field of galaxy evolution for many decades. If two gas-rich galaxies exchange a glanc- ing blow, rather than a head-on collision, the encounter may give birth to one or more smaller galaxies known as tidal dwarfs, rath- er than a large merger remnant. Dwarf gal- axies of this type are predicted to form when gaseous material that is tidally stripped from one of the larger galaxies condenses to form a gravitationally bound stellar system. The stripped gas may be highly enriched, in which case the resulting dwarf will have an unusually high metal content for its stellar mass. Galaxies formed in this way are also expected to have very little dark matter. October 2018 However, it is difficult to ascertain the past history of any particular dwarf, and identify- ing tidal dwarfs in the process of formation has been quite tricky in practice. A team of astronomers from Australia, Can- ada, Argentina, Italy, and the United States have used GMOS at Gemini North to obtain long-slit