A Systematic Search for Detached Tidal Dwarf Galaxies

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Our home galaxy, the Milky Way, is one of billions of galaxies in the Universe. It is a flattened disk of stars. The Milky Way is on a collision course with a similar disk galaxy, the Andromeda galaxy. Such gravitational interactions between galaxies change the structure of the galaxies. Tidal forces during the collision produce long streamers of stars that extend hundreds of thousands of light years into space. These are called tidal tails. Concentrations of stars in these tails resemble the small dwarf galaxies observed near the Milky Way. Some tidal dwarf galaxies may separate from their parent galaxies to become independent dwarf galaxies. Alternatively, tidal dwarfs may disperse with time with their stars being spread throughout intergalactic space. A third possibility is that these tidal dwarfs may fall back into their parent galaxy. The number of tidal dwarfs that detach from their original galaxies is not yet known. The investigator seeks to understand the remnants of these galaxies created during interactions and test whether observations of these dwarf galaxies be used to understand the history of galaxy formation. The investigator will employ undergraduate students as research assistants. These students will be trained in data analysis, problem solving, and scientific techniques. They will be encouraged to present their results at local and regional conferences. This experience will better prepare the students for careers as scientists, teachers, or data analysts.The investigator will compare the tidal dwarf galaxies near nearby interacting galaxies and a control sample of isolated disk galaxies. Ultraviolet, visible light, and infrared images will be searched for possible tidal dwarfs near these galaxies. The properties of these objects will be compared to those of other dwarf galaxies. The results will be compared to computer simulations of tidal dwarf formation and evolution. The final list of tidal dwarf galaxies will be made available to the public. The results of this project will test theories of galaxy formation. Galaxy interactions were more common when the Universe was younger. Tidal dwarf galaxies cannot be easily studied in more distant galaxies. However, they can be easily studied in nearby interacting galaxies. The investigator will use archival data from the infrared (IR), ultraviolet (UV) and optical telescopes, including the Sloan Digitized Sky Survey. The interacting galaxy sample includes 46 nearby pairs of galaxies with tidal tails. The control sample is a set of 39 normal spiral galaxies. The images around the targeted galaxies will be searched for possible tidal dwarf galaxies. The UV/optical/IR data will be compared to models of aging stellar populations to determine the average age of the stars in these regions and the total mass of the stars. The galaxies in the sample have a median distance of only 44 megaparsecs; thus, the survey will be sensitive to regions with star formation rates of 0.001 solar masses per year and stellar masses of 100,000 solar masses. The numbers of possible tidal dwarfs around the interacting galaxies will be compared with those near the normal spirals to determine whether there is an excess near interacting galaxies.