Gemini South Adaptive Optics Imager (GSAOI)
Measuring the Bulk Motions of Galaxies with Surface Brightness Fluctuations:
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It is widely accepted that the evolution of the large scale structure of the Universe is driven by dark matter. Understanding this dark matter continues to be one of Astronomy's great unsolved problems. Measuring the bulk motions of galaxies allows us to map the overall mass distribution of the Universe in a way that is independent of the luminous matter in galaxies. Each galaxy whose motion is measured serves as a test particle of the gravitational field around it. With large numbers of accurately measured objects it is possible to reconstruct the mass distribution of material in the Universe. Unfortunately, this has not been easy - since the first results of 15 years ago of the "Great Attractor", the field has been littered with contradictory results and findings that are still not understood. The heart of the problem has been finding a way to obtain large numbers of accurate distances for galaxies with Hubble velocities between 0 and 10000 km/s. GSAOI, with its excellent spatial resolution, can make significant progress in this field by measuring H band surface brightness fluctuation distances to hundreds of galaxies in this range. Already surface brightness fluctuation has been used at optical wavelengths to probe motions out to 2000 km/s, but this work has been hampered by the fact that much of the action happens beyond this limit.
H band surface brightness fluctuations provide distances accurate to about 0.12 mag, and are limited, in the case of GSAOI, by contamination from globular clusters at Hubble velocities > 8000 km/s, not by photometric uncertainty. Using observations of approximately 100 galaxies in the direction of the Great Attractor, the location, mass, and extent of the Great Attractor could finally be ascertained by looking at the motion of galaxies on all sides of this object. An additional survey of approximately 500 galaxies out to 6000 km/s across the whole sky would provide a new scale measurement of bulk motions in the current Universe, and provide a measurement of the scales over which dark matter clusters. |