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Galaxies and Cosmology

One of the most powerful ways of testing cosmological theories is to determine the three-dimensional distribution of matter, in other words, how galaxies of different types are clustered. The gravitational forces that led to the formation of galaxies in the early Universe arose both from ordinary matter, which we can detect with our telescopes, and from dark matter, which we can't. By studying the distribution of galaxies over the sky, we can calculate the sizes of the forces that produced them.

Galaxy Clustering

To make an adequate map of galaxy clustering we plan to make an ultradeep survey of 1200 square degrees to magnitude 27 in the g band. There is no hope of measuring redshifts of the faintest galaxies spectroscopically, so we will perform the survey in four wavebands and use the measured colors of the galaxies as a guide to their redshifts.

Gravitational Lensing

Another powerful method of studying dark matter is by using gravitational lensing. Light is slightly bent when it passes through a gravitational field, irrespective of whether the gravitational field is caused by dark matter or regular matter. We can use this effect to measure the total mass in a galaxy cluster. Although gravitational lensing sometimes produces spectacular effects, it most often shows itself in subtle distortions in the shapes of galaxies. By looking for correlations among the profiles of large numbers of neighboring galaxies it is possible to make three dimensional maps of the distribution of dark matter in clusters.

Other Galaxy Research

Other extragalactic projects that can be performed by Pan-STARRS include an ultradeep survey to probe the formation of elliptical galaxies, studies of dwarf and low-surface-brightness galaxies, and a program to identify far-infrared sources from future satellite surveys.

 Spiral galaxy

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